Moderate Oil Seepage from Strut - Normal?

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I maintain a 2006 Prius for one of my friends. Back at about 85,000 miles (about 5 years ago), it was discovered during an alignment that the front struts were showing a small amount of oil seepage. At the time, we decided to leave them alone and monitor the condition. At the recent 120,000 mile service, I decided to go ahead and replace the two front struts. The oil seepage had increased a bit, but was still "moderate" by Toyota standards. As reference, I have attached some pictures of the strut in question (both sides are the same) and the Toyota strut replacement criteria as per TSB# 0145-11: Untitled by The Critic, on Flickr by The Critic, on Flickr by The Critic, on Flickr Toyota Strut Replacement Criteria: Screen Shot 2015-07-05 at 12.42.35 AM by The Critic, on Flickr Here are my observations/questions: 1) The struts were still performing acceptably at 120k - which was when they were retired from service. Between 85k and 120k, the struts showed some degradation in performance, but the difference was not huge. 2) New struts did not provide a significant difference in performance. The ride quality improved slightly and body motions were a bit better controlled, but the difference was not discernible by the owner. 3) In accordance with the Toyota bulletin, this strut was displaying "level 4" seepage - which is considered moderate oil seepage, but does not yet require replacement. From my past learning, I was told that anything other than a light film of oil is considered "failure." What I am not understanding is -- how can a strut "seep" a significant amount of oil and still be working just fine? What do you guys think?
 
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I think the damper is leaking oil through the shaft seals. 1. How was the performance measured? 2. If the ride quality improved slightly and body motions were a bit better controlled. Then it would appear that there was a significant difference? If they were replaced with OEM units then the valving will be the same. So you will not magically of gained high performance dampers for no reason..... 3. On an OEM shock I would describe what you have as light oil seepage. The manual calls it moderate. This is a matter of semantics. How can a strut 'seep' a significant amount of oil and still be working just fine? I would consider the amount of oil in your pictures as an insignificant amount of oil on an OEM shock. A shock cannot seep a significant amount of oil and still be working just fine. If it was me. I would wipe the shock clean and put it back on. On the dampers I own I would have the seals replaced if they had any visible oil leakage. They are high performance dampers. Not OEM units.
 
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Originally Posted By: Critic
3) In accordance with the Toyota bulletin, this strut was displaying "level 4" seepage - which is considered moderate oil seepage, but does not yet require replacement. From my past learning, I was told that anything other than a light film of oil is considered "failure." What I am not understanding is -- how can a strut "seep" a significant amount of oil and still be working just fine? What do you guys think?
It looks to me like they have degraded to to what they refer to as level 4, the tube under the spring seat is stained but it gets washed away with rain. They know how much oil is in the shock at initial fill say hypothetical 400cc they also know that the shock/strut will still function satisfactorily with 380cc. They know the size of a 20cc stain on the tube. IMO this is nothing more than a way to avoid warranty claims and keeping a part in service until after the warranty has expired. industry standard practice is if it weeps or leaks its defective and should be replaced. Their quick draw of the TSB pistol probably saved them a another very costly recall.
 
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Critic, nice and well researched write-up. Herein my state, visible oil is a registration fail, as there's no telling what's happened before or after. I agree with Trav that a published "severity index" is a deferral to post warranty for a big part of the bell curve, and will serve as "due diligence" should someone get killed in the middle, between logged services. Dampers will still function to the point that oil and piston cease to meet.
 
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Here's another data point from a 2008 Camry V6, with 62k: 1) Left-front strut - Level 2 leak: LF strut leak - stage 2 by The Critic, on Flickr 2) Right-front strut - Level 1 leak: RF strut leak - stage 1 by The Critic, on Flickr 3) Right-rear Strut - Level 2 leak: Right-Rear Strut Leak by The Critic, on Flickr Similarly, in this case, there's significant oil leakage. The shock performance on this car, at least from a driver perspective, has some noticeable degradation but by no means was it dangerous. Most drivers would still be okay with their performance. So far, this has been my conclusion-- 1) Level 2 and Level 1 oil leakage are definitely indicative of reduced performance (or soon-to-be). 2) However, the shock performance is unlikely to have deteriorated to the point of being dangerous, so this is usually not an urgent repair as the vehicle drives acceptably. In many cases, the priority of this repair ranks somewhere between "necessary" and "nice-to-do" depending on the tire wear and the vehicle performance.
 
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This is interesting to me as I have never seen a damper leaking oil until a Buick a few weeks ago that came down from up north. Is this something that is common? Regional? It never gets cold where I live.
 
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Originally Posted By: CBR.worm
This is interesting to me as I have never seen a damper leaking oil until a Buick a few weeks ago that came down from up north. Is this something that is common? Regional? It never gets cold where I live.
How are your roads down there? I doubt temperature has much to do with it, but I'm sure the driving conditions do.
 
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