@Don McErlean There are probably people with a much more qualified opinion than mine who can comment on Marx Motors , but I just think they are made simple and made well, clarifying here I am referring to the simple 4 wheel variants or double reduction ones ! ... just a rudimentary design made well with no real adjustments necessary, about the worst thing that will happen to most people is the need for an armature clean and brush maintenance, which is really simple a trio of screws and 2 nuts and you are there in 2 minutes, rarely needs nothing more than a quick scrub with a fibreglass pencil and maybe a cotton bud with alcohol. Brush retaining springs are simple as and auto adjusting , even the e-unit if it has one is just a spray with contact cleaner, same as the manual reversing contacts
Just built well, non-complicated, nothing that needs gauging or finicky adjustments .. unbolt, clean , re-bolt, run !
9 times out of 10 even an old one just needs a drop of oil on shafts and it will run. I just like them because simple and well built beats technical and bean counter cost cutting every time.
Mr Marx knew what he was building and got it right early on and stuck with it basically 
Change for change sake affects too many things in this world , I don't need a toilet seat that cost $10,000 and has user customisations and selections , I just need something to stop my bum hitting the water ! 
