if it's a capacitor it will measure an open circuit, you'll have to remove from the cct to test if it's a cap. There could be a cap in series with the output to block DC voltages going to the solenoid which makes sense. What do the two sides of mr 50 connect to? One is the diode?
my money is still on it being a precision resistor for now..
Also that stripe on the diode means it's either a zener or a schottky. But not a power diode, so you will need to replace it with the correct part, not something generic.
Being a zener diode would make sense, in combination with the precision resistor would make a constant current source to prevent the solenoid overheating etc.