SLAM Doors to latch? With NEW latch
 

Ever since I got my 1984 300TD-T the doors have to be SLAMMED to close completely (I had 300SD and 1980 300TD years ago that latched perfectly with no effort at all) . I replaced the weather stripping on my drivers door and it got even worse. Luckily, the 4 bolts that hold the striker plate on were very easy to remove and didn't strip so I played around with it's positioning, but that didn't work. I then replaced the entire door lock striker with a brand new one. It now takes even more effort to have the door close completely. It latches into the first catch effortlessly, but not into the second. I've tried numerous different positions of the striker and the weather stripping is also on perfectly.
I have noticed that when it closes in the first position, you can see that the door sits a hair lower than the rear door until you close it all the way. I'm sure this has something to do with it too, just don't know how to remedy it.

Have you greased the latch assy? I've found that lack of lubrication is probably the main reason the striker disintegrated.

No I didn't. I didn't think it was necessary since it was brand new.

Have you played with shims? The tapered pin has to go in the hole on the striker PERFECTLY if you want an easy latch. If it's off, even by a fraction of a millimeter in any dimension, it will require a slam to close the door.

I'll dive into all these ideas tomorrow. Thanks for the input.

Is the plastic striker intact? That's usually the problem and is frequently caused by lack of lube on the door side.

This...

On the pillar, the round eye the pin slides into has a little plastic ramp.

If that ramp is missing, the door will need force to latch.