Case 1835B problems

[Toocheap1835B]

Hi everyone, I have a new 1835B. I have never worked it that hard. There are many small issues I have. All charge lights were on when I got it. I changed filters and all but one light went out but one sending unit has the wire broke off so that may account for that. The kid I got it off of was a friend but also cut a lot of corners. He had not used a lot but not ever changed any filters. He also used AW-68 hydraulic fluid instead of the 10W-40 and HTO. He didn't let it warm up much. He said the right side wheel motor leaked a little into the chain case. It was running oil out of the wheel and was pretty full and contaminated. I have a couple of questions that are not anything in the manual. Sometimes when I used it, the steering arms would get very hard to push and seemed to push back against my hands. It would push hard on one arm the it would spread to the other one. If you pulled back and let it it set for a second it would be fine. What would cause that? I used it pretty hard one day and that was really my biggest problem. Also it would sometimes not move forward and was kind of loud. I think it was cavitation. Is there a better fluid that avoids foaming? The hydraulic lines got pretty hot. Any ideas on the "pushing back" resistance? Do you suppose he blew the motor deal from pushing too thick, cold oil? It has 2170 hours and is actually in pretty good shape. I paid him 2800.00 for it. It runs great and never really lost any power. It is now in my shop and I'm going to go through it top to bottom. I am going to put a quick attach on it. Thanks in advance for any help you can give.