hi, although Haynes etc say it can't be skimmed it can, had mine done last year, if your HG has gone it would be wise to have the head pressure tested to rule out damage to it as often they crack intenally, i had a 2nd hand head fitted last year cost was around £900 parts and labour, thats why i advised pressure testing the head as you dont want to build it up again only to find the head has cracked, pressure test costs around £40