I had leak issues with Reinz and other aftermarket valve cover gaskets; switched to MB and no problems.
My 1980 300SD was doggy off the line similar to yours. Checked all the same stuff and finally confronted the ALDA unit. Did not want to mess with screw so removed ALDA and installed a transmission drain plug washer to shim it approx. 1/16” higher. No problem off the line anymore.