Only way is to dismantle ands see if it is simething as simpole as a failed seal or something more disastrous.
It does bugger all good but sympathies
You could try a specialist forum. Google throws up the following:
http://farmingforum.co.uk/forums/showthread.php?21198-JCB-3CX
http://www.classicmachinery.net/forum/viewtopic.php?t=7661
http://www.fwi.co.uk/community/topic/jcb-3cx-torque-converter-problem/
XXX, December 2015