I, too, have played this for many years.
A: 51
B: 421
C: 421
D: 421
feels most comfortable to me. I would always play the bass and up-beat this way unless the up-beat spanned an octave or more, in which case the bottom note of the up-beat would be fingered 5. At bright tempos, I find the 4th finger is much better at grabbing the bottom of the chord rather than having to carefully position the 5th. Isolated bass octaves are mostly 51, except when the bass plays a moving line as in the latter half of measures 2, 4, 6, & 8. These I would generally finger 41, 51, 41.
I found it very helpful to work out a fingering strategy in advance to oom-pah bass that I can live with. That way, I don't have to give it much additional thought, i.e., the fingerings are automatic and only certain exceptions require conscious attention.