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?