There is a hole at the top of the playfield which works properly sometimes, but other times actuates too weakly to pop the ball out, and sometimes nothing at all. The coil is a D.40 S.1200, which is cross-referenced with the Williams 26-1200, which I have bought to replace it with (the replacement coil officially says "AO-26 1200").
So I've take the coil out of the housing and measured its R, L & diode:
0.011 each way
The replacement shows basically the same readings.
I'm not sure how to interpret the diode reading, other than to presume that there is a "short" through the coil itself, so a proper read on the diode is impossible.
I'd like to think of everything I should try before swapping out the coil. I suppose I could try checking the elements on the driver board, but after that I have no idea.