Can someone tell me where I may get spare gaskets for a Servowarm Supreme Plus Boiler system?

The gasket on the manifold to the left of the boiler has start leaking. I have tightened the four bolts and stopped it, but I suspect it will soon need replacing. Fitting a new system will be a problem as I live in a 4th floor flat, and access to provide balance flues will be difficult and expensive. Also redecoration in the living room would be needed if the existing system is removed. So keeping this one going is my preferred option. Any advice or guidance would be appreciated.