Here's a good Question...

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I know someone that has an older vehicle with about 170k on it that runs perfectly. Plugs are dry when pulled and inspected and the engine (GM) has plenty of power so it makes no sense to do a reman engine really at this point. But, the rear main has recently started to leak a little. They change the oil every 5k and have to add a quart every 3k or so. They have been running Amsoil (since about 75k) like I do on mine and the thought has come up that maybe the Amsoil is so clean that it contributed to the seepage. So, I think they are going to try some Bar's Leak or something similar to see if that helps the rear main to stop leaking. So, what's the general consensus on continuing to use Amsoil in this situation? Think it would be better to keep using it, or switch to a conventional oil? Just curious what the local oil experts here on the board recommend.
 
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Personally, I would ditch the additive and use a high mileage oil. Mobil 1 HM or Pennzoil HM would be my personal choices. Others here have had great experience with Valvoline Maxlife blend.
 
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I've talked to a few folks over the years that claim to have had good results using Bar's Leak. Isn't this stuff supposed to swell the seals a little? Isn't Mobil 1 high Mileage still using a synthetic? It's a V6 so what would work best, an 10W30? .
 
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They say the transmission needs to be removed in order to do a rear main seal which is going to cost a lot.
 
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Try a high mileage oil for a couple OCI and see if it reduces or stops the leak. The problem isn't that the oil is synthetic, but he seal might have shrunk some over time. High mileage oil has conditioners that help keep seals working. My old Camry had 307k when I sold it. It had several very minor oil leaks. I used some Mobil HM oil for 2 consecutive oil changes and it very noticeably reduced the amount of oil used between changes.
 
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Since the oil leak is fairly minor, I'd suggest switching to a high mileage oil. High mileage oils have special additives to recondition & swell the oil seals & gaskets in the motor. I'd suggest Valvoline MaxLife Synthetic Blend. Mobil 1 Full Synthetic High Mileage is my second pick. Valvoline also makes a MaxLife full synthetic but it's extremely difficult to find in my area. Anyway, these oils will help reduce the oil leak and maybe even stop it completely after while. I don't suggest using any additives like Bar's Leaks. I don't figure it would do any harm, but a good high mileage oil would be best in my opinion.
 
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OK, so apparently the high mileage oil contains additives that conditions the seals right? Seems like they could use the Amsoil and just dump some additive in. Question is, what additive does Mobil 1 put in their oil? Do they sell a stand alone additive? And, what would be wrong with using Castrol GTX High- Mileage? Lots of folks like Caster oil .
 
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Originally Posted By: CT8
5,000 miles with Amsoil?
Right! Unless it is a short tripper the oilcould go much further, even if it is not SS. As far as the seal, 1 quart in 3000 miles isn't much so just drive it....get the seal fixed if it is worrisome, but adding something to clog the leaky seal only masks the problem and won't cure it. A HM oil might fix it but if it doesn't he is right back where he started as well as having switched away from his chosen oil.
 
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Originally Posted By: Rockrz
They say the transmission needs to be removed in order to do a rear main seal which is going to cost a lot.
Once again please Year, make , model and engine
 
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It's a late model vehicle with a one piece rear main seal... so the tranny is going to have to come out to do the job which makes it a high labor cost job. They're going to run high mileage oil for a while and if the leak doesn't get better after a while they'll revisit this situation and decide what to do at that point. .
 
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Update... apparently, Lucus makes an additive that works for seeps like this cause I'm hearing this is what was used and not the leak is gone. It appears that unless the leak is really bad, then one should use the Lucus stop leak to prolong blowing all that cash doing the repair
 
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I've heard that it's not a good idea to run synthetic in an older engine as some claim it can cause it to start leaking. Synthetic supposedly runs much cleaner than conventional oil, er so they say.
 
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I'd just switch to any name brand high mileage oil (including amsoil if that's what it has to be) and live with it. Especially if it's running good and not obviously burning the oil or ant head gasket issues. I don't think it's ever been proven that a synthetic oil was the problem in a high mileage engine.
 
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