I'm concerned. yellow gunk under oil filler cap...

Check your PCV and hose, will form moisture if it's plugged, worst case is a cracked head, blown head gasket. It's not normal.

 

It's plenty normal if you do short distances in the cold and your engine never warms up. The four years I lived in AK, I drove maybe two miles one way to work. If I didn't get a good 50ish mile drive in once a week or so, it would get moisture related sludge in the cap/filler.

The causes you mention could also be true when it is not short trip/cold engine/not burning off moisture related.

we're all replying on a 7 year old thread too.

 

Using better oil will cure this. I make a lot of short trips and don't see any goo using AmsOil Signature 100% Synthetic oil.

 

Just made the switch to sybtheic. 5W-20 for the winter. But will keep it at 5w-30 after this