If you're talking about the main seal that prevents oil & fluids from
leaking, then I've got the same problem with my 98 Sentra XE. I've tried
the soft leak sealant fluid and it only worked for a short while. I've had
estimates in VA & WV and have been told the same in both states, that due
to the location of the seal it's going to be a huge pain to repair. B/c of
the location, the engine has to be pulled from the car the seal replaced,
the engine re-installed. Approximately 3 days labor + parts = $2000 range.
We may be better off just to buy new cars...
Probably not the answer you were looking for, but hope this helps! ~c