Its my guess, the spool valve is leaking.
Just replaced the spool valve seals in my 753. Mine were dripping but In the cold weather they leaked worse. I left my machine outside in the cold for the winter and during that time It probably leak 2 gallons.
My 753 makes a rattling noise at idle. I hate it. Not sure if it's the bearings. Problably not. I think the the noise comes from slop in the gears. I took the belt of and felt the back lash and turning the pulley side to side about an inch.
Need to pull gearbox out