i opend up a spare bosch pump i have and its got about 1mm off varnish in it , i had left it full of fuel before storage year and a half a go with bio diesel in it i think, so whats the best way of removing the varnish , or will have to strip the pump and cleen bit by bit
will have to strip the pump and cleen bit by bit 
That would be my approach... too many fine passages to risk a loose piece of varnish stranding you by the side of the road some day.
Good chance to reseal while you're at it... and if it's been sitting that long it may well be due.