My winter diesel is my old B275. I retrofitted it with an active circulation pump and heater, and the block will be up to actual operating temperature in under an hour unless it's really, really cold. I also installed 12V pencil glows from a Mercedes to replace the old series connected loop glows, and it starts like it was summer.
The Deutz came with nothing but an external oil pan heater that nearly caught the whole motor on fire when I tried it. Too much oil had leaked and covered everything in tar. Fun times. Are your oil heaters internal? Are they in the block or the pan?
My key works the same way, but nothing lights up on the dash. There is a good chance the light is burnt out/wiring messed up though as the dash is a nightmare. What is the symbol on your dash light, none of the German symbols look anything like our traditional glow plug symbol.
I don't really care about the diff lock much, especially if it's weak. However I would love to be able to stop the PTO. Mainly as it would be really nice to be able to shut down the baler and rock picker without killing the tractor engine. Interestingly I left it set to "off" yesterday while baling, and it disengaged once when the bale got heavy. I ran it disengaged for about a minute to try to clean off the clutch plates, then re-engaged it and finished the bale. Unfortunately I could not get it to shut off again.