Hi Gary.
Yes I would double check the jubilee clip/spring clip, the old crimped clips can be re-used and are the best to use, if not then use a jubilee clip the straight through ones with captive nut.
https://www.the75andztclub.co.uk/for...d.php?t=241484
It could also be a weak pump from the start, I would only ever fit a pierburg UBP even a good used one is better than these after market pumps.
https://youtu.be/ExC6zuyNI3A