I purchased a GTC 52-2 tiller for my JD2210. I'll be changing the transmission oil soon and can't find any of the oil or grease recommended in the manual. For the grease I use Deere's SD polyurea grease in the U-joints, but for the oil it recommends either a straight 90W or 80W/90. One of the recommendations is Shell's Dentax 90, which I can't find. According to Shell's website, this oil has an API GL-1 rating. I can find several brands of GL-5 (or 4) in 80W/90, but nothing in GL-1. The manual doesn't specify an oil rating. Any recommendations? Thanks.