My 97 OB needed cam cover seals and oil pan seal at about 200,000 kms, an easy job. The 97 cam cover and oil pan uses a tube of silicone for sealant.
I agree with nipper on the rest of the stuff you should do while the engine is out (ie water pump, main seal, oil pump seal et al) and to NOT to get any of your gaskets off of eBay.
Definately a weekend job too.
Cheers and good luck!
sb