I have a B2620 I purchased new this spring. I went to my dealer this weekend and bought everything to do the 50 hour service myself. I asked my dealer which hydraulic fluid to put back in and he said UDT would be fine. In fact, they don't carry the SUDT. He said that nobody buys it and they haven't had any reason to believe that the SUDT does anything the UDT doesn't. We live in SW Oklahoma where it is 100+ degrees all summer long and it seldom drops below freezing for longer than a day or two. So my B2620 which according to the manual came from the factory with SUDT will be getting it's fluid replaced with plain ole UDT fluid. Just wanted to pass along what I was told. If anyone thinks my dealer is way off base, please feel free substantiate your claims. Thanks in advance.