However, when i drained the fluid i only did so from the drain under the left foot clutch.. looking on this forum it sounds like there is a plug in the sump as well. (Would explain why only two gallons came out - which seemed way too few). Furthermore, the guy gave me what he said were Hyd filters, but after removing the current filter and trying to put it on, it doesn't fit. I think it's the engine oil filter. So, the old filter is back on as well. 

My questions are: Are there two plugs on a series IV? Would you drain the whole system again, change the filter and add fresh fluid?.. I'm telling myself (to justify saving money) that since they had a leak, they kept the fluid pretty fresh - but at the same time I don't know what they were putting in there so i might have a mix now. Also, what oil should I use if/when i drain it again?

Thanks!