Worcester Expansion Vessel External Leak!

[SteveZodiac]

Having had WB out last week to replace diverter valve, gas valve and w to w heat exchanger on my 28CDi, I've now got the boiler pressure going crazy which looks like an expansion vessel problem. I re-pressurised it a few weeks ago so it's probably gone completely. In fact, it seems to be weeping water from the seam at the bottom of the EV. Has any one seen this before?

Also, do any gas parts have to come out to replace it? Service manual says gas to water heater exchanger has to come out, but I can't really see why.

If it's definitely a CORGI job any idea how much it will cost me?

Thanks.