AlfredB You should only need to lubricate the cam 4 times per year, after backflushing with cleaner 4 times a year. But you should remove the shower screen every 2 to 3 days and clean it, behind it and the inside of the group around the dispersion disk. Backflushing with cleaner doesn’t effectively remove the residue that builds up in this area.
The reason for the lever stuff is all groups can be made differently (tolerances in cam and followers), pump switches adjusted differently. On many machines people use group lever in the middle position when pulling a shot (usually if plumbed) so the water pressure can apply pressure to the coffee, as a sort of preinfusion, it doesn’t work on all. The logic is the top brew valve can be open, the implication of which is not good for air getting into the system if the lever is in this position when it cools down and the boiler, boiling dry if switched on in this position. As the “middle position” really isn’t a thing by design….don’t use it.
It will do your pump no harm at all to run for 15-20s against a blind filter….in fact running it for longer than 15s does very little extra cleaning. The main cleaning that is done, is after you put the lever down and vent the group…..so the time you wait until you raise the lever again to continue the backflush, is very important and should be 30-40s, allowing the cleaner you flushed down there to do it’s work.