Tractor Repair: Castlegarden Ride-on transmission problem., hp tractor, drive belts

Question
15.5 HP tractor mower with Twin deck loses power after cutting for a while. Opened the transmission and checked no blockages or breaks inside. Cannot get the little manual selector to operate (it works like a clutch to disengage the gears that allows the tractor to be moved manually). It is possible to do this at all time. Is this my problem or is it something else? Any suggestions with regards the level of oil in the box, I'm not convinced its completely full, despite my best efforts?

Answer
 Subject: Castlegarden Ride-on transmission problem. Question: 15.5 HP tractor mower with Twin deck loses power after cutting for a while. Opened the transmission and checked no blockages or breaks inside. Cannot get the little manual selector to operate (it works like a clutch to disengage the gears that allows the tractor to be moved manually). It is possible to do this at all time. Is this my problem or is it something else? Any suggestions with regards the level of oil in the box, I'm not convinced its completely full, despite my best efforts?

Hi John.
If only I could see what you are looking at life would be a lot easier.
Loses power after a while ___ over heating?
Do you mean the engine –or the cutting ability if it’s the blades not doing their job after a while I am wondering if the drive belts are slipping? Can you check the tension?
SWITCH ENGINE OFF BEFORE DOING ANY OF THESE JOBS OF COURSE.
How old is it –does it need a major over haul?
As to the oil level only the manual can confirm this.
MARTIN