If it was my truck I wouldn't even consider dropping the oil pan to replace a rear main seal if the truck is 45 miles from my shop. I'd get it towed the 35 miles. I think that the chance of the seal just going bad all of a sudden is wishful thinking.
I would do some more diagnostics before tearing things apart. Maybe pull the distributor and use a drill to run the oil pump to get a better look to see if can find a source for the oil leak.
