Joe,
I have a '99 PT185 and it has the weld in the same place as you described. It is just after the riveted keel reinforcement or protection "V" strip and is about 4" long.. I also bought mine used in 2001. It never leaked in that area until this spring. I noticed water would pour out from inside the "V" strip for awhile and then it would drip for days. I finally flooded the boat from the bilge area (front of the boat down on the trailer) until it started to leak. Mine did not leak at the weld, but was coming from inside the riveted "V" strip that is over the keel. I assumed it must have been rivet leak I could not see under the "V" strip.
I since have installed a 8' KeelShield and have not had anymore water problems since. The KeelShield is "not" designed to cover up or fix leaks, but so far so good. It has been on since early May of this year.
I would appreciate if you would let me know what they find at the dealer inspection. Carl