These plastic are not wearing out significantly faster than metal ones, although if your locos are running mostly under heavy loads and on automated layouts with lots of starts and stops, they will need replacement faster than metal ones.
Changing worn gears in a Märklin loco is not particularly difficult (I have done it for decades and you can learn that "skill" in 5 minutes..) you just need a small press with the proper inserts (depending on the axle diameter, but a 2 mm one will solve 95% of the cases)
And you'll need to have a few small wooden blocks tu support the chassis and insure to set the gear axle properly aligned with the press.
Marklin introduced these Delrin gears in a feeble attempt to reduce the noise in their locos.
I say "feeble" because it was just another "cheap shot" of the penny-conscious Schwaben in Goeppingen to solve a basic manufacturing problem.
For the longest time, Märklin gears have been stamped out of a steel ribbon using a shaped die .
This is the cheapest way to produce gears.
Cost being primordial, precison is only a second consideration in "toys" .
But gears can only be "silent" if the teeth are cut following an accurate profile (involute épicycloïdal) which guarantees when truly perfect a friction free transmission of the movement as the surfaces of teh meshing teeths are **rolling** on each other instead of **sliding** , the latter generating friction
It's the friction from that "sliding" that causes the noise.
Simple.
Some locos were quieter, some noisier.
Hit and miss.
If you were lucky enough to get a loco with (all new) gears from a brand new die tooling, the profile was way better than after the same die would have cut of few thousands of the same gears.
So plastic gears being formed by plastic injection was a much cheaper process, and with a somewhat "better" precision...
But...in practice since Marklin continued to mix plastic meshing with metal gears, the *rubbing** (and the noise!!) was still there
, and the plastic gears would wear out eventually (sometimes faster as metal ones..) especially under heavy loads.
In my years of repairing Märklin locos, I started to cut my own replacement gears, in brass, on a milling machine using a set of Mod 0.4 involute cutting gears.
This allowed many restorations of locos that went back to their owners running way more silent than originals.
Nowadays practically all gears are either plastic or machined on CNC controlled gear cutting machines.
Precision and consitency are better and consequently, Marklin locos tend to be quieter and smoother.
I guess we have mostly learned to love that "noise" that is so characteristic of good old Märklin locos!
