Lefever with issues

[TARNATION !!!]

Hi. A friend who knows I can do a full service on Parkers, presented me with a family gun and wondered if I can fix it. It is 1912 built sidelock ejector gun. The issue is that the right trigger does not move. Lots of possibilities. I removed the side plates and opened the barrels and chambered two snap caps. Left trigger fired. Right did not move. Opened the barrels and both snap caps were crisply ejected. Repeated the process while watching the left side internals. Hammer engaged sear and remained in cocked position. Then watched right side. Hammer will not engage the sear so when barrels close the hammer moves to fired position. That’s why the trigger does not move. Several possibilities come to mind - all related to worn parts. Maybe hammer, maybe sear, maybe cocking rod , maybe maybe…. I want to completely disassemble but have zero experience with a Lefever. Don’t know any pitfalls that await me.

So, has anyone got hints, a schematic, disassembly instructions.

I can wing it but prefer to avoid flying springs or a finger owie or other problems a little knowledge could avoid.

Appreciate any help that’s out there.

Thanks
Jack

Top image is the offender with hammer in the fired position when it should be cocked. Bottom shows left side cocked as it should be.