Head gasket?

Hi all, recently I have noticed my heating going cold and having to top up the water....due to oily deposits in the water I suspect a Head Gasket problem?......
My question is can anyone advise me on a good place to have it repaired and approx cost?
I live in Plymouth.

Thanks in advance

Mike Harding in Bovey Tracey would be my choice - about 30 miles from you mind.

Mine was £850ish.

But i needed a new head and other stuff too.

having mine done at the moment £300 inc genuine head gasket and skim and pressure test(Cheshire area)

Thanks for the replies and info