is it easy to put a second expansion vessel on volkera linear 24?

hey,After finding some one who had the exact same problem with their volkera linear 24 on this site (Pressure dropping to 0 after the heating has been switched off) I tryed all the fixs', I dont have any leaks on the whole system so i ruled that out. Then i pumped up the E.V to 0.7 on the gauge and topped it up to 1.5 then ran the heating and turned it off, Same again down to 0. I then drained the e.v and checked the flexi hose was'nt blocked, re-pressured it again , Same again. So ive come to the conclusion that the vessel is knackered, also because ive topped up the system to much and the pr valve is now leaking from the pipe!! volkera want £90 for a E.V, so is it easy to put a second E.V on and replace pr valve my self? can i get a longer flexi pipe to reach the new E.V? will it be the same thread? what capacity will i need? so many questions!!!! dont know where to get the answers! any help would be brilliant!