The old starter motor died just before Christmas so I purchased and fitted a Britpart (Part No RTC5225N) replacement, with the aim being to refurb the old one in slow time.
The new starter appeared to be rather slugg'ish, but would start the engine. A few weeks ago, it would hardly turn the engine, so I removed it. Testing it across a battery it turned so slowly that the bendix didn't even throw. The starter was returned, and a replacement sent.
This replacement arrived last weekend and before fitting I tested it across a battery. It all worked fine and so was fitted. The first start was fine, but further starts again appeared slugg'ish. Suspecting that the battery could be going flat, the battery was removed and put on charge last night, ready for refitting this afternoon. Yet again it turned father slowly.
All connects, including earth leads have been checked and cleaned with no improvement being made.
Am I missing something / should be looking at something else, or is it just another suspect starter motor.....
Thoughts are welcome.

Test it across a battery again. Can't think of anything that would cause a starter to fail prematurely other than serious bashing about or misalignment.
Could be Britpart is the problem? Try an oem one or a recon known make.

Test the battery, putting it on charge isn't the same as knowing the battery is good.

Thanks for the info I'll try again tomorrow