Yea 30W would be fine.

I found TO-4; Transmission Fluid; SAE30 locally, that should do. Too bad I need 7 buckets.

see if you can buy a 44 gallon drum yes it a big outlay but it works out cheaper some times. and with a drum pump its easier than pouring out of several smaller drums if you want to get fancy you can add a flow meter nozzle and dispense just the right amount.

and you have a drum to reuse as a fire pit, scrap metal bin, use for waste oil even rinse with fuel and use it for storing bulk diesel (provided its a steel drum) note some places wont let you fill them due to the perceived fire risk due to static buildup and if it suddenly discharges. yet they are happy with those plastic diesel pods which do generate static.