Hello Steam Jon. If you still need a reverse unit and funds are tight, I can offer a couple of options. First of all, I believe your RS-3 uses a 600-0103-001 Electric E-Unit, as shown in here. Go to Supplement 27 and open it to pgs 1-5 thru 1-6. I believe that's your loco. If so, Lionel still sells that E-Unit for $16.50+shpg, and if you're super-patient, you could wait until November and hope they have their 50% off parts sale again.
Option number 2 is that your old (presumably fried) e-unit should be easily repairable - email me for further discussion, my email is in my profile.
