rear main/oil pan leak got worse, move to 10w30? or switch to conventional?

1 quart of oil over 3 months isn't horrible. I had a Cadillac that lost a quart over a few weeks 😂

Throw a bottle of AT-205 or BlueDevil Rear Main Seal in the oil and run it for the duration of the oil change. I can just about guarantee you it'll seal up. (It won't stop anything up, it swells the gasket.)
Have you tried Blue Devil Rear Main sealer? I know many guys who have used this product for rear main seals and it worked well. No special oil is needed & the product is guaranteed to work or your money back.

Link to the product page-
I was just gonna recommend Blue Devil Rear main sealer too!

I’ve heard many great things about those. It seems like they really do work. Won’t hurt to try it out. Just use any 40 weight oil with the blue devil and run it for a couple hundred miles, and see if the leak slows down. I would use 40 weight since that blue devil stuff seems pretty thin. I might be wrong.

After you add the blue devil stuff in, clean the bottom of the engine as good as you can. You’ll never know where exactly the oil is really coming from especially with how much oil you’re losing.

I like to use acid wheel cleaner. Just spray it all over, and wait 30 seconds. Then rinse it off with a pressure washer, no need to crawl under there and scrub things. Just spray then rinse. Acid wheel cleaners won’t damage nothing, as long as you don’t let the chemical sit for too long on rubber and plastics.

Drive for a couple weeks with the blue devil, and try to look under the engine at least every other day.

Now you’ll really be able to see where the leak is coming from, and also you’ll see if the leak is slowing down at all.