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Potentially buying a 99' Nissan Maxima from some friends. It has 160k miles on it and they are looking to get the "good" private party value from KBB for the car. The car is a manual, if that makes a difference.

I had them take it to our shop to get it looked at before the sale just so there would be no surprises. The shop said that it appears both the front and rear crankshaft seals are leaking some oil. They advised that I would need to keep an eye on the oil level if we were to purchase the car.

I've spoken with my friend (who is more mechanically inclined than myself) and he agreed that we could fix the front seal ourselves before the sale. The rear seal, however...

I haven't laid eyes on the leak myself, and even if I did I don't yet have enough experience to know what I am looking at.

If we replace the front seal, what is the likelihood that the rear seal will fail? The cost of that repair is easily 60% the KBB value of the car. I'm sure that there are many factors that go into this, but if the seal doesn't have a major leak can I nurse it along for 40 or 50k more miles?

What indicators should I look for that would point to the seal failing? It's also possible that my friend would lower the price of the vehicle so the repair could be completed, but I don't want either of us to throw away our money.

Looking for an educated guess from someone with more background than myself.

(P.S. Seems like there aren't tags for "crankshaft" or "seal")

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When ever you have more then one oil leak on an engine, especially at higher mileages, check the PCV for good operation. A poor PCV valve or hoses will allow crankcase pressure to cause oil leaks. Although you can expect really good mileages from modern oil seals, any seal on any engine can start to fail and it would not really be possible to give a definite life for any particular seal. Needless to say, most rear crank seals last the lifetime of the engine.

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Crank seals generally don't fail catastrophically - they fail rather gradually, leaking more & more over time. You can get by with a leaky crank seal for a long time before it really MUST be replaced; you just have to keep an eye on the oil level.

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    It's bad to leave them leaking when you have a manual transmission, as you will contaminate the clutch with oil, causing slippage. If you get it fixed soon enough, you'll have no worries. With an auto, I would agree with you.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 20, 2014 at 1:37
  • The clutch is on the opposite side of the flywheel from the crankshaft - if enough fluid pools in the bell housing to ever REACH the clutch, you have more problems than just a crank seal. A transmission input shaft seal, yes. Not a rear crank seal, though.
    – TDHofstetter
    Commented Aug 20, 2014 at 1:49
  • Wish I could mark both responses as answers! Thank you for the information :)
    – Shrout1
    Commented Aug 20, 2014 at 14:59
  • @TDHofstetter ... The problem is, the oil leaks down the back of the flywheel, then is centripetally thrown against the bell housing/dust shield and will splash back up onto the clutch. When enough is thrown, it gets all over the place and will cause the friction disk to become oil soaked/contaminated. At that point it will start slipping and no longer be usable. I don't think I've ever seen a dust cover which does not have some sort of drain hole in it, so it should never get to the point of reaching the clutch assembly (because it will all be out on the ground).
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Aug 20, 2014 at 21:58
  • I've seen motor oil flung centrifugally in large quantity against the inside of the bell housing, enough to make it REALLY GREASY inside, but it tends to just gradually run down (rather than splash) to the bottom. I've pulled nice clean dry clutches out of those cars - did an MGB last year that was like that. AWFUL HORRIBLE mess inside the bell housing, but all the clutch parts were nice & dry. Motor was toast (thrown rod, broke out BOTH sides of the block, full of that nasty Castrol crap).
    – TDHofstetter
    Commented Aug 20, 2014 at 23:49

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