Seals are $10 from Jon Goodman and take only about an hour to put in (most of which is cleaning out the old gunk). I do it as a matter of course on all the bodies I buy. Then I don't have to worry about when I'll need to do it!
After you do the foam the back should be snug, and will feel overly tight the first couple of times.
All my finders are bare metal...I just buy the diopters and flip my glasses up when shooting.