I am pretty sure that it is now under Llandegfedd Reservoir.
I have looked at old maps of Glascoed and compared to present day maps. You can find the old maps on
http://www.old-maps.co.uk - search for Panteg on the old maps site and then look to the far right hand side - in the centre of that side. You should see Pettingale Farm - next to Greenpool farm.
If this is hard to spot, you could always search for Glascoed on the ordnance survey's "get a map" site
http://www.ordnancesurvey.co.uk/oswebsite/getamap . You should see Llandegfedd Reservoir. Pettingale would have been at the first point of the resevoir that you would reach if you headed directly north-east from the Water works on the Panteg side of the reservoir.
Failing that, you would find Pettingale Farm by keeping looking south from Maes Mawr in Glascoed and east of Ty coch (which lies on the Panteg side of the hamlet)
Alistair