Fred,
When you mentioned the hose collapse and blistering it brought to mind many of the sealers that are added and available in the recharge R134A market now. This seems like a hose material issue, but I'm not sure if the degrade is all heat related, there may be incompatible chemistry and materials involved.
The other thought is with a repair most often you pull a vacuum on the system for an extended period, I was thinking perhaps that might help collapse and blister a weaken hose and possibly cause some interior delamination. Hard to know for sure, looking forward to knowing what you learn on this one Fred.
Later Ed