Is there any way to lubricate old 4.5V 6216m2 engines (these grey round ones)? I have 2 from my childhood, and they still run, but have trouble starting and make an awful 'whining' sound from time to time. I see no way to open them, and I haven't found anything through google about opening them. (I was hoping to see videos, but can't even find a text description...)
You don't need to open the motor to get the lubricant in. Electric motor oil is thin enough to work in if you hold the motor with the shaft uppermost and slowly rotate the shaft by hand while squirting a small amount down the shaft.
Don't use a lot - try a small amount, and see how well it works. Add more if needed.
(this one I found on Amazon)