Andy Hall wrote:

If you have weeping valves it is because they are worn out or were crap
in the first place. You can go round tightening them and packing them,
but IME it doesn't last.

I would have a blitz and replace the lot - it's do-able easily in a
morning. Also, I would recommend getting good quality valves. They
cost a little more, but when you consider the time and cost of replacing
inhibitor after draining to fix one valve, it's worth it.

I inherited a system with the valves being female at both ends (rad and
pipework). Does anyone know if such things are still available? When I
have to do it, it's going to be tricky to change the connectors on some
of the pipes:-(

Douglas de Lacey