Crank Bolt Loosening

what is your crank and bb combo? perhaps you're mixing JIS and ISO and so the cranks aren't sitting very tight on the spindle.

so a campy record bb should marry up fine to a pair of old shimano 600 cranks ?
jis vs iso
i've mixed a matched JIS and ISO a couple of times, only change the chainline.

i don't grease spindles, they are meant to bind to the crank and with grease they don't as well.