Just bought the official GG repair kit for a 2012 TXT and was surprised to find that they don’t come with the round pin that connects the shaft to the drive so if you are changing yours make sure you don’t damage the pin when removing it. 
Rang around and nobody has the pin in stock in the U.K. 

Is it not just a standard spring pin/spring cotter pin, sometimes called a roll pin ? (Hollow tubular pin made from spring steel with a split down its length allowing for it to be a spring fit through the hole in the shaft & gear). If it is then it should be easy to source from an engineers suppliers just by specifying diameter & length. And it’ll be cheaper than the price loaded brand labelled item.

The water pump drive pin is a solid pin, rather than a hollow roll pin.

The original GG part number is MT280218009 for the pin, and the original Waterpump shafts were MT280218006 - which was just the shaft with no pin, but then in 2004 GasGas updated the part so it was delivered with the pin, this was then part number MT280418006.

So check your invoice, you must have been given one of the old 2002-2003 one without the pin.

7 hours ago, arnoux said:

The water pump drive pin is a solid pin, rather than a hollow roll pin.

The original GG part number is MT280218009 for the pin, and the original Waterpump shafts were MT280218006 - which was just the shaft with no pin, but then in 2004 GasGas updated the part so it was delivered with the pin, this was then part number MT280418006.

So check your invoice, you must have been given one of the old 2002-2003 one without the pin.

I phoned both GasGas main dealers here in the U.K. and they said that since KTM took over the kit comes without the pin. John Lee motorcycles had one left ( MT280218009 ) so I bought that one. The reason for change was a corroded pump drive shaft but the old pin was a very tight interference fit and I thought a new one was a better option than trying to reuse the old pin although it did come out with a bit of heat and not so gentle persuasion !