Got twin 1997 502 EFI's with rough 400 hours. The surveyor mention after about 10 minutes at WOT there was a little "weeping" around these gaskets and he mentioned it would be a good maintenance decision to replace these gaskets. Part numbers would help but also want to know how hard is it to replace these? I am fairly mechanically inclined. I have done impellors, water pumps, fuel pumps, plugs wires, etc.

If they are leaking on the outside they are also most likely leaking on the inside. That will wipe a motor out quick. Easy to change unless you snap a bolt off in the manifold and then you have to deal with that.

Can't get link to mercruiserparts.com to work. Part # 27-863726. Here it is on a site I buy from.
http://www.wholesalemarine.com/p/27-...27-863726.html

Both engines or just 1?

I thought it was just the starboard engine but I am gonna replace all of them on both. How many gaskets for each riser? Also, compression and everything came back very good, so internally ok, but the surveyor is very anal (good!) and said it would be good preventative maintenance. I am also doing, plugs, wires, impellors, fluids, gimbal bearings, bellows, batteries.

oh, and u joints

As long as you don't have any spacers, 4 gaskets will do it. 8 gaskets if you have spacers.

I dont know if i have spacers or not. Everything is stock and it does have corsa silent choice.