If it's not leaking that much during oil changes, just run it and top the oil off when it needed. You can buy a whole lot of quarts of oil in what it'll cost to fix it unless you can do it yourself. We've had oil leaks from the pans on this one and the past gm car(aurora) and just adding oil seems to be the easiest fix. If it has been sitting that long too, I imagine the oil leak is going to look a lot worse than it really is.
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charlie
black 98 gtp sedan, 222,000 and running great with the new used tranny!
zzp 3" d/p aluminized
dhp 1.0