Welcome aboard DAN!!!
Looks like you (or your repair shop) is in for nice little project. Brakes are never fun on any large tractor and these Ns are no exception. (especially with filled rear tires in some cases!) The oil leak on your 2N is probably simply saturating your worn brake pads and causing failure. The shop will probably use SureSeals to fix this problem. You will want to replace your brake shoes and lining assembly, possibly gaskets and also check alignment and set. These pads are asbestos so no sanding or burning the oil off to preserve em.
Get a new set - 9N2019 should be around $65.00 wholesale for both rear wheels. They might charge you ~$125 for brake shoes, pads, & sureseals etc and then labor on top of max of 6 hours. ($40/hr x 6hr = $240 + $125 = $365) --- That seems kinda high to me for a brake and seal job but I am giving you a high "city" quote. Honestly, I would say less labor time so you would be good at a quote of less than $300 --- say $250 total to do the job. Remember that you can overhaul the entire engine with magnaflux, boring, honing everything including all new components for about $750 total out of the door. ($350-400 will get you complete new engine kit with all components for these flat4s)
Heck these tractors go for $2500-3000 completely restored -- Dont pay too much!
FYI, The oil is most likely coming from inside the axle which is lubed by the crown gear turning and dripping oil into a small collection dish in the casting and in turn runs down to the end of the axle housing. That is where the oil leaks out from the brakes on alot of these 2Ns. Either that or various points on the axle seals are bad and if your full with 234D fluid, you will have alot of fun getting flooded. If there are leaks at the point that the lift arms bolt to the tractor, it is good to replace those gaskets while you have the axle housings off. You may need to replace the bolt studs & springs also. Check em for heavy wear. (heck you got it all off now!)
Let me know if you need anything else.
Andy