If it's caster locked I highly recommend the Glycol based antifreeze in a crock pot method..
Lots of threads here on that..

I did mine in a crockpot I'd clearly marked NOT FOOD SAFE with a giant magnum marker..
Set the pot to low.. disassemble the motor as much as possible.. tie all the bits together with a wire fishing lead or thin gauge music wire and drop it in the bath.
Check it at 4 hours. See how it feels drop it back in if it needs more.. Dry it out with compressed air lube with ATF.

I've done 5 motors that were locked up from 15 years in storage.. They all came out fine and run great.