300SEL - Distributor Piston
I've been there. Lucky forr me that i measured the clearance before I removed it. However, as long as you were careful with the plunger, you should be able to fix it. You can get a Bosch fuel injection manual(available at many bookstores) or preferably the CD MB manuals. These should give you the plunger rest cleanance. It also appears, , based on what you have told me, that you need to readjust the mixture setting on the flowmeter air sensor. This is easy to do and is spelled out in the manual.