Q: Truck leaking oil after adding product.

The oil additive is supposed to cover any mechanical part the product touches excluding seals unless they need replaced with a covered part. This means your seals by themselves are not covered. The oil pressure gauge reading H all the time may be an oil pressure sending unit is defective or the oil pressure relief valve is stuck on the oil pump. I suggest having the oil leaks checked and the oil pressure system checked for problems. I would recommend having a mechanic, like the certified ones at YourMechanic, come and check it out for you to see if this is the only problem.