Hi Hess
Here user of Märklin M tracks since 1961 and in digital from 1988 until 1998 when I switched to C Track.
There is aboslutely nothing wrong with any piece of M track (including those diamond crossings), provided, of course it is not bent or in bad shape and this goes with digital operation too (no restrictions). So "unbend" tracks and rectify rail joiners so that they are straight and make a very strong contact as when they were new.

One can say (I do) that M track is very nice with a wink to our childhood.

The M track restrictions:
- early switches, because of the large lantern are not compatible with modern long coaches
- even with the best kept M tracks, trains dance on the track especially on DSSs and switches
- it is noisy. Märklin tried different solutions: foam to cut at will or rubber blocks at screw holes with little results
- the solenoids are current hungry
- old Märklin rolling stock (all metal) have a tendency to have couplers touch the studs making shortshort-circuits (which may disturb digital operation). Simply adjust the couplers height.

Cheers
Jean