STEP AWAY FOR THE WD40, SIR!! DROP IT!
Well, WD40 pits metal over a prolonged period, & since pot-metal is softer & has big pores, it would probably be even worse.
I would avoid it. Place the parts/spray it with in naphta or gasoline instead for a couple of hours.
Avoid spilling on the wood.
Once taken apart remove rust/grit with fine steelwool.
Oil carefully with a high quality mineral oil, such as sewingmachine-oil.
If you feel that you must use WD40, clean it of with a rag dipped in naptha/gasoline after the work is done.
If it comes apart fairly easy, then follow Neos advice, & you should be safe, but please remember, pot-metal is very brittle & doesn't react like other metals do.
If it is frozen, you should be very careful. I learned this the hard way, with a Columbia portable tone arm...
addendendum:
Please excuse my impoliteness; Welcome to the Board! Always nice to see a new face
