Lots of divers over here have very old Achilles SIB's. I wouldn't say they're bulletproof, but they seem to hold up quite well. Most of the ones I've seen nearing the end of their lives are due to fabric delamination, top layer wear, or reinforcing weave failure. Glue failures can generally be repaired.
As with most boats, older means you'll be doing a lot more to keep it on the water; how much is too much depends on what the up-front discount is worth to you.
jky
__________________
|