Intermittent starting problem

My 110 300RTdi is getting a little temperemental starting. Most times she fires up first go, but every now and then a few goes aere needed, with just a loud click when trying to start. Leave it a few minutes, swear a bit, and it works fine....

Sounds similiar to issues I and a few others have had.

1) Check all earth straps, including the battery terminal post. Pay particular attention to the strap from near the starter motor to the chassis. Take them apart, clean, copper grease and reassemble

That will probably cure.

If not:

2) Check battery is well charged

3) Starter motor - check all cables secure, but could also be solonoid on the way out

If not:

4) Check ignition switch - less likely but they can give problems

Personally, suspect an earth issue as prime suspect

my money is on solenoid contacts.

I've got a new spare battery if you want to try it - 20 miles away.

Is it when it's been left for a while? Could be leak off pipes?

Not when left for a while, and sure it's not the battery, as it turns nicely when it does fire, and generally fires staright away, just the occasional problem. Feels to me like a loose contact somewhere, or something sticking in the solenoid... but I know very little about electrics.