Extensive parts diagrams available here:
http://septimus-spares.co.uk/cold-pressure-washer/karcher-home-garden/k-620m/
I BELIEVE this is the section that switches off the motor if it thinks the washer outlet is not open (Note I said it thinks the outlet is not open. It may be faulty and not letting the motor cut in when the trigger is operated)
http://septimus-spares.co.uk/cold-pressure-washer/karcher-home-garden/k-620m/excesscurrent1/#parts
I BELIEVE this is the area that would be lubricated - the gearbox:
http://septimus-spares.co.uk/cold-pressure-washer/karcher-home-garden/k-620m/transmission28/#parts
Available as a PDF here:
https://www.pressureparts.com/mmDEV/PDF/karcherparts/K620M%201.973-680.0.pdf
Of course, you'd have done a search and found all that anyway - wouldn't you? Took me about 2 minutes.
XX
December 2015