I can convert Stenlights to run off my batteries, and replace Stenlight LEDs. I have other spares but no lamp leads or lamp PCBs.
Stenlights I have took apart have had PCBs fixed with 2 sided thermal tape so not removable without destroying them. LED replacement fiddly working inside the lamp, but possible.
Unable to help in any other way.
Mr Superterminal, I strongly recommend trying your lamp on someone else's battery, or on a lab PSU set to 8V output (make sure you get the polarity right!). From what I know of Stenlights, it sounds like a battery fault.
Is it the old shrink wrapped design, or the later plastic cased. If the former its probably water got to the management PCB, they damage on the slightest scuff.