Lumbersawyer has a good question. The SM420 synchros work best with mineral oil. Hypoid gear oil or synthetic oils are too slippery for the synchro to work well and any oil with sulphur may attack the bronze synchros. If you are not sure I would drain your oil and replace with 90 wt mineral oil. I did that with the SM420 in my COE and it had an immediate, albeit slight, positive effect. Your 2nd gear synchro may just be worn out which happens from too much down shifting into second.

Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix