I'd agree with Donald, try removal with the engine hot.
Also I'd get confirmation that the base of the glow plug is in fact ceramic.
I know things could be wildly different, but I'm looking now at a glowwy that came out of my old 2.2 RTDT Lag 1
PN on the box 77 00 861 906
It certainly doesn't consist of any ceramics.
I enjoy cooking with wine......Sometimes I even put it in the food!
Currently in hondo's garage:
Toyota Auris 1.6 V-Matic SR. Red hot, toasty feet.