My bike was registered in 88-E reg.I presume the later ones must be different??When I lifted the barrel,it left the base gasket intact in place.I put another XL base gasket on top of it,as per GB FAQ site,to lower the c.r. slightly.Both gaskets were identical.This is the only XBR I'm familiar with,so I can't comment on earlier ones.The barrel and piston were bog standard XL600 items. Have you had clutch problems??