I recently got a nail in each of my front R-4's (at different times). I have a tire plug gun but was out of plugs so I put in a can of fix a flat and refilled with air. I later bought plugs at NAPA and plugged the tires but the fix a flat worked fine. I'm sure worth a shot and would cost much less than removing, repairing, then refilling.
Can you see or hear where your leak is? Is it definetly a rim leak, perhaps you ran over a nail. I found mine buy airing up the tire then raised it off the ground and hosed down with water. Its been since March so you may have run over something sharp.