A right side wheel cylinder is probably leaking & oiling the shoes. Especially if you replaced the shoes without replacing/rebuilding the wheel cylinders. Pull the right wheels & drums off and look for the nasty oily one.



Some of my crap:
1963 C-30 flatbed dually 292/SM420
1965 C-10 LWB fleet 250/column shift 3 speed
1965 C-30 9' stepside 250/SM420/4.10 gears (my DD)

Website I made for my crap:
http://www.66submarine.com