engine trouble

I have about 1100 SMOH on my IO-360 (2000 TBO).
Compressions are all 70 or above.
There was only a tiny bit of metal at the last oil change.
That was shortyly after I bought it, at which time I also put a spin-on
filter adapter on.

The engine has been running great, especially lately.
However, my mechanic was fighting a nagging problem.
It seems the seal where the crank case halves come together leaks.
Mine is/was leaking right on top of the engine.
It was very disturbing for a while, but my mechanic managed to stop the leak
with some silicone.

I understand that taking it apart would be very expensive, so I've been
pricing an overhaul.
Looks like about $17K for an overhaul.
I'd really like to milk it out closer to TBO.
I'm wondering if I should continue to ignore the problem, as long as no oil
is leaking, and the engine is running fine.
It's been about three months since any problems, but I don't know how long
it will hold.
I've been flying a couple hours per week with not even a drip.

Your suggestions would be appreciated.

Adam
N7966L
Beech Super III