This is a 98 model so it has been used a lot. Picked it up cheap. Worked good, then wife had surgery and It sat for 4 months. Boom will not move now. I have checked the electrical controls, Overides and control switches ect. They all seem to be flowing electric as they should. The boom does nothing. Hydralic pump is working. I am thinking it is low on Hydralic fluid. Sounds simple; I have been all over it and cannot find a fill point. There is a hydralic tank inside the trunk the boom sits on. Filter is directly over it. That tank has a plastic cap on it, when you take the cap off it appears to be only a vent. Got the Manuals on it. No where does it show how to add Hyd fluid. It says there is a sight glass on the boom but I dont find one. Goggled it an found no help there Help Please.