http://www.ebay.co.uk/itm/Fuel-Tank-Tap ... Swq5lTp8Ka
Cheap, generic taps are all over the worlds EBay's, BUY one that`ll flow freely, (measure the flow by timing a known volume of petrol through it and compare what the stock TRX flows). Then, make an adaptor plate from stainless (so it won`t corrode), fit a generic tap and once n for all sort your leaky tap out!
In fact, here ya go, a Yamaha fitment, a tap that should work fine for a TRX: http://www.ebay.co.uk/itm/Gas-Fuel-Tank ... Sw~uhUnQV3