Tranny lube??

[65ChevyC20]

I have a 65 Chevy C20 w/ a 4 speed manual, the shifting is getting a bit hard to get into gear. I need to change the tranny lube but I have no owners manual to tell me what to put in the tranny. Can I use a synthetic lube or should I just go with factory lube, whatever that is. Hopefully someone can tell me here. Thanks

[rwgregory]

If it's getting hard to shift have you checked your clutch adjustment lately? If that's
ok, try putting a few ounces of Pro-long differential & manual trans additave in the
gearbox. That stuff worked wonders on the 4-spd. in my Mercedes Coupe. I thought
I needed new synchros but after a gear-lube change w/Pro-long it now shifts as
smooth as butter. FYI, any good petroleum based gear oil will work just fine in your
trans. Whatever better auto parts stores carry. Good luck.