'93 Park Ave would not start...discovered positive battery terminal corroded and would not stay in side post battery...... got a new terminal, cleaned the battery, terminals etc...... replaced terminal with brand new terminal a week ago...... last night would not start again..... discovered the tip end of the brand new terminal end nearly disolved away with corrorosion and would not stay in battery....what would cause a brand new terminal to corrode away in a week?

How old is the battery? Often poor connections or even venting or small leak will cause quick corrosion.
Try coating the terminal with Vaseline, or use a battery terminal protector spay & see if that helps.
Side post are not the best, as you try to keep em tight, they can strip.
Was not long of owning the PK Ave before I got a sealed AGM battery and moved to a top post solution.
AGM batteries are fully sealed & do not vent= no corrosion.

The battery is fewer than 2 months old.

Acid leaking at the terminal?

Side terminal Delco batteries often suffer from side terminals disconnecting at the connection inside the battery - even brand new ones. Your putting a new bolt-terminal on the outside may have just wiggled the connection good enough to make it work for a while - then the connection broke again. Replacing that particular battery is the only fix.

Then again, maybe it is just a little corrosion on the inner threads and you just need to take a wire brush to the inside of the terminal. That would be great news.

I've never seen a top-post battery post disconnect on the inside (except when my best friend hit mine with a freakin' 16lb hammer).

ss like acid is leaking around the battery post ! try those felt things that goes on the battery posts, they seem to help by keeping the acid away !