1984 190D Manual Transmission - issue

[Chewable]

So I have a 1984 190D. It originally came with the 2.0 engine and a manual 5 speed.
The rings were bad when I got the car so I pulled the engine and swapped it with a 2.5 out of a 1987 190D that had a bad transmission. I used the flywheel and clutch that were there. The clutch was in great shape.
I have driven the car for a couple of years and it is by far my favorite car.

Last night I started getting a grinding noise from the transmission and after making a turn I could not get into second. I was able to limp the car home. If I was able to get to 4th everything was smooth.

A few years ago I found another manual in the local junkyard and was able to get the transmission, pedals, and shifter. Someone took the flywheel, clutch, and driveline.

I did not give it much thought at the time, but I am now concerned that the flywheel maybe too light for the 2.5 and it has slowly caused damage.
Does anyone know what the weight difference is between the 2.0 and 2.5 flywheel?
I want to fix this car and keep driving it, and I feel I have enough parts to get it back.

I also have another 190D, but it is an automatic with a transmission that does not go higher than 2nd. I have been on the fence about trying to put that other manual I have into it. But now if I damaged the engine in mine I may pull the engine from that one and replace mine.

[Frank Reiner]

1) Inspect the shift linkages for missing or damaged plastic bushings. Ensure that the bolts that secure the shift arms to the transmission shift shafts are tight.
2) Ensure that the clutch is releasing properly.
3) If the external inspections are all good, remove and open the trans for inspection.
4) The results of the inspections will be the best guide to solutions.