Trans Linkage
 

This one has me puzzled. Yesterday I put my 84 300SD 126 in park and it didn't catch. I also noticed the shifter has gotten real loose. I'm correct in assuming this is simply a bushing problem?

Could be. They do wear and fall out/fail. It's a relatively easy fix. Parts are cheap.
http://www.peachparts.com/shopforum/diesel-discussion/243638-w124-shift-lever-bushings.html?highlight=bushing

I'd bet grommets. The one on the shifter is pretty easy. The one on the transmission is a bear. I just replaced mine. I ended up taking the lever arm off the trans to putting the grommet in. The lever arm only goes on one way so you don't have to worry about getting it on in the right position. There is a 10 or 8 mm bolt holding the arm on the trans. Also a cup of nearly boiling water helps soften the grommets to make them go in much easier.