I bought a used ws5223kawe 52" stander last week which I did a full tune up on. The last step I need to do is change the filter and fluid for the hydrostatic system. I know I use mobil1 15w50 for it and I have read a owners manual for a newer stander online. the problem I have is in that manual it said to fill the hydro oil tank to the bottom of the oil level port and mine either doesn't have a oil level port or I cant find it. so how much oil do I put in it?