I have heard from other technicians sometimes the valve spool can have a slight burr on it & jam.
BT say that valve for side shift & tilt in the main valve block isn't replaceable & there are NO replacement parts listed for it either.
I do know from a colleague it is possible to take the spool out & remove the burr to stop the spool jamming BUT be warned you risk ruining the complete valve block if you get it wrong / break it in the process.
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