Timing adjustment

I have a 1989 mk1 gti cabrio (dx engine i think).
I have changed the timing belt and i want to adjust the timing setting, and although i have removed the distributor clamp and bolt the distributor is seized solid. To date i have applied WD 40 with no change.
Any advice or suggestions would be appreciated.
Many thanks in advance.
Jim.

What I did to mine when I first started to wrench on it.
I soaked my DiZ in PB-Blaster which is a Creeping Oil.

The issue is that the o-ring had seized to the block and the Diz.

What worked for me, was to use a Vice-Grip around the base of the Diz as tight as you could lock it.

Then use a small Ball-peen to smack it a bit left or right
A bit until it freed up.  WD-40 doesn't creep.

A 50/50 mix of Acetone and ATF fluid mixred in a small jar, and dribbled on the Base of the diz for a couple of days.

I did the Chisel and hammer on my 92 and the base, and that shocked it to turn a bit, then I grabbed a pair of Channel locks on the base to move it back and forth.

When I had this on my 93 I used the vice-grip.  
I did remove the diz from the block and cleaned the hades out of it and spread Copper grease on the thing, including the groove of the diz, and the block..

Take care of the removal so you make sure which way to rotate it when you bull it out of the block as the Rotor
is a good positioner to check the settings.

Hi Briano,
Many thanks for your helpful and comprehensive reply.
I was reluctant to use too much force as i thought that the distributor unit might be fragile but I have to get the unit rotating somehow so I will take your advice and give it a go.
regards,
Jim.