Motorcycle Repair: exhaust system, rear cylinder, stock system

Question
I have a 1993 FLHTCU (Purchased used 2 years ago)and have had the rear cylinder exhaust pipe break 3 times in the last 18 months. It is a stock system with kerker mufflers. I was given a set of used pipes when the first break happened (cracked at the Y where it goes to the left side). It then cracked in the same place 3 months later. I then bought a new pipe from the dealer and 1 year later it broke just above the Y at the junction of the front cylinder pipe and the rear. New gaskets and hardware were used for each repair. I now am running it with a welded pipe(purge welded)and not able to trust it for a long run. Any tricks to keep the stress out of the pipes in these potential breaking areas when installing? Tried installing loose and tightening a little at a time to avoid stresses. Also this last time I warmed the exhaust system up (ran the motor) and loosened a little then tightened everything down. I've done that twice and am now just crossing my fingers. Any advice would be greatly appreciated. Just can't afford a whole new exhaust system.

Kris

Answer
I have never run into this problem before. I have seen pipes crack over time, but not as many times as you have said.
I would check all my motor mounts and make sure they are tight, so you are not getting excessive amount of vibration.
Good luck and happy riding
Mike