I'm in the process of determining what the problem is with the GTX in terms of its poor/no starting due to slow cranking, even with a fully charged battery. 

I suspect (or hope!) it is just one of the negative grounds somewhere that is corroded and needs cleaned, but I can only find one and the trying to find the other one has initially proved unsuccessful.  A thought came to me today though, that in order to test if the grounding is the problem or not, I could just run a jump lead from the negative terminal to a ground point (with the terminal connected of course), and that would then ground the battery if the original ground is ineffective. 

Am I right in thinking that?  If so, that would quickly tell me if it is a problem with groundings or not, and if it makes no difference then I'll know it is something more serious such as the starter motor or a seized pulley etc...

4 hours ago, jmurray01 said:

I could just run a jump lead from the negative terminal to a ground point

Sounds right to me. A good, heavy, copper jump lead would help. Possibly to one of the bellhousing bolts, or some substantial & clean bit of casting there. Take great care not to short it to the +ve at any time though!

I had slow cranking & sometimes fail to crank, it was the solenoid on the starter motor. I could hear it click, but it made bad or no connection to the motor.

I did a temporary fix twice by removing the solenoid, and giving it a good clean: Got it going for a while, and proved the point.

Eventually I managed to source a replacement solenoid for about £22, but it took a lot of hunting.

 

 

20 minutes ago, Tdci-Peter said:

Sounds right to me. A good, heavy, copper jump lead would help. Possibly to one of the bellhousing bolts, or some substantial & clean bit of casting there. Take great care not to short it to the +ve at any time though!

I had slow cranking & sometimes fail to crank, it was the solenoid on the starter motor. I could hear it click, but it made bad or no connection to the motor.

I did a temporary fix twice by removing the solenoid, and giving it a good clean: Got it going for a while, and proved the point.

Eventually I managed to source a replacement solenoid for about £22, but it took a lot of hunting.

 

 

Thanks Peter, I'll bear that in mind.  It's a toss up between that, the alternator or the P/S pump being seized.  I looked at the starter today and it actually looks fairly new, like it has been replaced in the last few years, perhaps as an attempt to fix the issue.