Weeping isolation valve on boiler return

[jono44]

Hi Everyone,
I recently repaired a Vaillant thermocompact 112. Isolated boiler flow and return and drained down so I could replace expansion vessel. Since refilling and pressurising and turning on the valves I've got a slight leak out of the valve (Ball valve area) and it doesn't want to stop.
Vaillant tell me that they don't have these valves anymore!
Any Ideas on how I might stop this leak? - I thought of maybe trying a leak inhibitor type solution in the system although I haven't ever had to use one before.
Any advise or recommendations would be much appreciated.
Many thanks,
Jono,

 

[REDSAW]

oh dear, yes they do that.
i have allways been told not to touch them for that reason.
would lsx work?.

 

[wnjswozo]

put some internal leak sealer in via a rad ,that will sort it,old worcester combi,s are the same .a pain