3 thoughts come to mind:

1. Are you absolutely sure it is coming through the pan and not leaking from somewhere else? Not sure what you have done so far, but if it were me, I would go through the other possible leak sources once again, before blaming the pan.

2. If you bought the Ragusa pan because the finned design assists with oil cooling, then coating it would degrade that somewhat as it would act as in insulator. If you already have adequate trans fluid cooling on your rig for what you use it for, and just bought the pan for some other reason, (Replace a damaged pan, increased oil capacity, etc) then this point is moot.

3. If you choose to coat it, I would be leary of coating a used pan on the inside --especially if it is porous. Getting all the oil out of the metal would be difficult, and any oil left on or in the casting could cause the coating to fail. If it's on the outside, it would just flake off... On the inside it could flake off an cause an issue with your transmission internals.

How much is it leaking? If it's just a drip or 2, I would probably just leave it and monitor my oil level, which is important in these coaches anyway. More then that, I would probably not coat the inside, if it was me. If it's a new pan, I would probably consider contacting Ragusa, as the best option would be to replace it, if it is weeping.