Keep blowing 20A fuse that allows me to start the car

My mechanic, John, says something about "stress" on the transmission when the vehicle is parked on an incline that he read on the internet. Never had this problem before. I'm trying different things: pulling up on my driveway and putting it in neutral, putting on the parking brake and then shifting to park. I've got about 10 fuses to experiment with hoping I don't need any major repair but I'd rather have a permanent answer. The only thing, once the fuse blows, on the dash board is the oil light. What needs to be repaired/replaced?