It still seems to be a solenoid problem to me. It was the banging on the top of the solenoid that finally got the unit to respond. Nothing in the starter will work until the solenoid piston moves to engage the starter power contacts. I have found on the old 220D that heat would adversly affect the solenoid operation. It also seemed that the cable contacts on the outside of the solenoid were sometimes affected by heat and I suspect various levels of moisture and corrosion. Just replacing the solenoid and using good contact grease helped a lot on the 220D.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150