I cannot replace 20th Primes smoke stacks!

Help!
I have a pair of long stacks for my 20th prime but I cannot get his shoulders apart to fit them.
I take the screws out, one large and one small but the two halves are still stuck together and I dont want to force them for fear of snapping them.
Has anyone else had this and how did you overcome it?
Cheers.
I have a pair of long stacks for my 20th prime but I cannot get his shoulders apart to fit them.
I take the screws out, one large and one small but the two halves are still stuck together and I dont want to force them for fear of snapping them.
Has anyone else had this and how did you overcome it?
Cheers.