I'm having a nasty feeling about your engine, 2nd pic on post 17, shows the primary shaft and chain. However it also shows the oil gallery tunnel connecting the oil pump to the main journals, this appears to have a large crack in it, whether the crack is weeping I can't say but it don't look good to me. I'd say something hard has hit it from underneath, possibly a part from the gearbox. If it is cracked through to the inside of the tunnel then you'll be losing oil pressure, even if it's not weeping you may be wise to consider having it welded because if it goes whilst driving the engine will most likely sieze before you know it, the oil pressure switch sits on top of the oil pump and this will be pumping fine so it may not light at all to warn you.
The clip you found looks a lot like a piston gudgeon pin circlip, there are 2 on each piston stopping the pin from sliding out, I've seen them with those little tabs on the end to make removing them easier, circlips tend to have eyelets, especially the gearbox circlips. It's been a long time since I've taken one of these apart but having done over 100 of them over the years I can't remember a clip that style around the clutch area.
