Welcome to the GTP Nostromo. I don't think engines blow up in GT3. Yes, you can use your GT1, but I would recommend doing Trial Mtn. Enduro and Rome Enduro. I am sure there are others you can do that I didn't mention. As for the oil, I raced the GT One in the first 7 races of the PD Cup. It needed new oil near the end of the 4th race but I managed to make it through without losing too much HP.