[Tom Goldman]

Like Joe said ,check voltage at the S terminal for drop.
Also dont rule out the starter relay itself.
I've had a hot start problem ,and the volt drop across the solenoid was 3 volts when it got hot ! .
I cut it open to see what the problem and was shocked by how cheap it was .
This was an Echlin, but it was made in China.
I now use a AMETEK /Prestolite metal case solenoid with silver contacts.
The p/n is 15-108 , it can sustain 200 amps continuous ,and 600 amps intermittent.
the photo shows what most Chinese relays look like inside , pretty poorly built for our applications.