Peter, if it is not a hot rated alt, then it will die again if pushed. That is what your 2nd repair guy is getting at, IMO.
The Next Step regs do push the alternator when the bats are down a bit. If the bats are never down much, what you have will work, possibly for quite some time.
The fault is neither with the reg, which is working fine, nor the alt, which is (now) also fine, but the fact that they are a mismatched pair. The reg is good for a boat
, but the alternator is less than ideal for the task it has been given (charging a house bank, right?) in your boat
. If you replace it, get a good hot rated alt, and you will have years of trouble free charging