I am considering buying a boat with an old (c. 1975) 115hp Mercury
outboard. According to the seller, it was rebuilt about 300 hours ago
and runs great. Assuming the basic checks came back fine
(compression, lower unit oil, etc.) and that it was rebuilt by a
reputable place, is an old but recently rebuilt outboard a good idea?
Put another way, is a 300 hour rebuilt engine comparable to any other
300 hour rebuilt engine, or does the old age add significant negative
issues?

Also, any guess as to the value of such an outboard?

Finally, is there some natural limit to the numbe of times you can do
a major rebuild on an outboard?