The gas 114 115 have a mechanical linkage for sure. So the diesel automatics of this vintage will have one too.

The gentleman that posted his shift issues. Disconnect the switch under the throttle pedal in case it is closed all the time. I do not think it the issue but just in case. I am assuming it has one without knowing.

Other than this I suspect the seals are dried up from sitting in the transmission. Since this is not experienced as much on the 123 transmissions I suspect they changed the seal material at some point. Again without knowing.

Try some automatic transmission aid stuff. It functions by expanding old seals.Needless to say make sure your transmission fluid level is accurate.

There also is a small chance the transmission filter is shot. Other than these things the transmission would have to be rebuilt I suspect. The seal expander also takes time to work properly. Usually as much as fifteen hundred miles in a driver. Improvement by the seal expander of any amount will indicate what the trouble probably was. Dried out seals in your vintage actually are fairly common.

I have even seen a mechanical engine shift linkage rusted off on a 114 gas car causing very early shifts. I guess again without knowing had it rusted off in the other position the shifts might have been very late.