Mobil 1 5W-30 synthetic is fine. I also have a 5502 with the GT530 engine and I also experienced the small oil leak. It is most likely caused by loose bolts holding the breather tube. I just removed the bolts but some blue Loctite on them and tightened them down snugly. Don't get carried away with torque.....that is aluminum you are dealing with remember. My bolts were so loose you could unscrew them by finger pressure. Known problem with the GT530.
Search posts on this site for help getting to these bolts. Most helpful.
There is a kit and instructions that Ziller carries to perform the repair which includes longer bolts and a gasket but I did not use it. That was in August 2015 and no reoccurring leak with just tightening the bolts.
Ahhh, I love it when my "throw in" questions provide a solution . . . but downcast at being outside the warranty window. Again.
Anyway, any links to specific instructions? The kit is on backorder apparently, but, also apparently, is not really needed. I did a search in the forums and find all pictures and links to them are gone. I did a quick eyeball of the unit but did not see the culprit.
I do have the engine pdf so can probably figure it all out, but, you know, a picture is a, well a bunch of words.