Look to buy a new trailer....
Thanks for the comments, guys.
My oil pan scrubs the tail of the trailer at the top of the ramps. It's a flat trailer (no dovetail), and that's probably the issue. This morning I a couple of pieces of 2x12 lumber, and placed them on the trailer bed at the top of the ramps. so that the front tires would continue up onto the lumber directly from the ramp. That raised the front of the car about 1 1/2", and that was enough to allow the oil pan to clear the tail of the trailer by more than an inch.
I'm thinking if raising the ball on the truck hitch about 2 " by simply removing the ball from the receiver mount and flipping it over. That might change the angle of the trailer enough to clear the oil pan (raising the nose of the trailer lowers the tail, thereby changing the ramp angle. I'll try that later today.
If I have to change trailers, I'm leaning strongly toward another steel trailer. I prefer a fully decked trailer, but the open bottoms do have their advantages. I'm really interested in that "Texas rollback".
...and the pricing on aluminum is eye opening.
Thanks again for the input.