I will answer this recommended oil question. Take your pick. The owner's manual for that engine specificies everything from 5-30 to 5-50. Also included are 10-30, 20-50, 15-50 and finally 10-40. It all depends on the ambient temperature range expected.

It's not the oil. I would think in terms of what else has changed. I would focus on the oil filter. Is the filter a Mann or Hengste (sp?). Or is it a McParts made in India? Also is the rubber o-ring properly seated?

I would put on a new quality filter and see what the result is.

Steve