...in case of future use for anyone:
O2 Sensor part no is 1B9-8592A 00 00 and is also fitted to the YW125 Zuma scooter (USA) and was for a while on the XP500 TMax. It seems to typically retail at about $170-190 in the States. Hence wanting to find a cheaper alternative!
The manual for the Zuma (excert below) confirms that it is Zirconia thimble type sensor with a heating element resistance between 11.7 - 15.5ohms.
I suspect that the heater element output is the main issue hence the need to confirm impedence of any universal type replacement.
Found this a useful source of info:
http://www.picoauto.com/applications/lambda-sensor.html
Of course, if funds aren't an issue then just forget all this and get a PCV & WideBand datalogger!!