"Check the tilt assembly on the front right hand side of the cabinet. There should be a tilt ball and sometimes it can be lodged all the way towards the back of it's assembly. This will tilt the game. Also check the tilt plomb. You can remove the plomb itself until the game is working"

Those assemblies are on the right hand side (in your picture). There's no ball in the tilt assy - so the switch should not be shorting. The way it works is that whan the front of the machine is lifted, the ball runs along the track and trips a switch. This tilts the game. The plomb looks fine.

There maybe another tilt switch in the baseboard or under the playfield.

I have a feeling that the bumper issue will be a relay. To find out which one, activate the bumper and watch which relay activates. As others have suggested - Dim the lights and look for the spark, or translate "bumper" into German and reference that with the realy.