Veloce ergopower 8 spd lever not engaging

ex-pat scot
ex-pat scot Posts: 939
edited June 2010 in Workshop
Old but nice serviceable 1st generation (I think) Campag Veloce ergopower shifters.

The rear (RHS lever) shifter is now struggling to engage.
The "upshift lever" (which is separate, behind the brake lever) turns freely on its axis, rather than engaging with the ratchet mechanism.
If I force the shifter forward (pressing it against the brake lever) then try and shift, the lever engages.

It feels like a simple "tightening up" exercise. But when I partially disassemble, I can't find anything obvious that could be tightened up.

I don't have a repair manual.

Does anyone have experience of servicing these, or information on how the internals work?

Thanks in advance
Commute: Langster -Singlecross - Brompton S2-LX

Road: 95 Trek 5500 -Look 695 Aerolight eTap - Boardman TTe eTap

Offroad: Pace RC200 - Dawes Kickback 2 tandem - Tricross - Boardman CXR9.8 - Ridley x-fire