The oil leak sure sounds like the pump-to-block gasket. This will be a very tedious job to fix, for the reasons Paul mentioned in his post. Not fun. Perhaps the OM61x engines used a flat gasket here? The later OM60x series have an O-ring that,
AFAIK, rarely fails (leaks).
The motor mount job is quite unpleasant and tedious as well. If you attempt this yourself, the FIRST step is a trip to the coin-op car wash with a can or two of engine degreaser. Soak the entire area, both sides, from top AND bottom, and blast it as clean as possible. Otherwise it's straightforward, just no fun. This is one thing that Mercedes fixed on the newer cars, they now have one-piece hydraulic mounts that are a piece of cake to replace - with no silly engine shocks and multi-piece mounting hardware.
I hope the mounts cure your idle shake. My '84 has a shake that I don't like, and is still there after new mounts, valve adjust, new rack damper, injector pop testing, and 2 cans of Diesel Purge. I gave up at that point!
Regards,