Dave wrote:

I think I should fix these, as some of the leaks are more serious if the
control on the rad is not screwed down fully. If the manual control is
not screwed down fully but removed, water can be clearly seen coming
around the pin on two or three of these. Hence I can't really use these
rads at all.


Hang on a minute - if this is a full series system, or if part of it is,
won't turning off one rad in the series part turn off all the rads in
that part of the circuit? (Equivalent to turning off a switch in a
series circuit)

Turn all the TRVs up high (with suitable placement of sponges/cloths as
necessary ) and see what happens.

Andy