SAE 10W30
The kind that you put in it
The transmission oil pan needs to be dropped, then you can disconnect the detent cable, remove the small bolt holding the sheath to the outside of the transmission then slide it out of the transmission. Be sure the o-ring is in good condition or just replace it when installing the cable back in.
85W90 gear oil.
C 20 Chevy has 160 HP with a 4 barrel carburetor and 145 with 2 barrel carb. Both @3800 Rpms and Oil pressure 40 at 2000 Rpms...Ralph Maldonado
The two bolts could have loosened up, or possibly there are two gaskets in there.
5w30
5W30
5W30 oil.
10w30 weight oil.
Drain the oil from your Chevy oil pan. Remove the oil pan retaining bolts. Remove the oil pump retaining bolts. Reverse the process to install your new oil pump.
5w30 or 10w30
The manual states 5W30.