Oh dear I have just discovered the stem is well stuckand truly and is resisting all attempts to release. Wedge has been knocked down, penetrating oil soaking for last few days but not budging. Perhaps it's not the worst thing since I have discovered a dent in the front forks which looks like a crush mark from perhaps a front light bracket being tightened too much. So this gives me the excuse to cut off the stem and replace the fork. Look out for a "wanted" ad soon. This is the first stuck stem for me, I will now check them all in future before I buy, although this was priced low enough that I would probably still have bought it.