[Brian]

Yes, I did sort out the problem....I tried another sender unit, but it too had some sort of issue, I can't remember. Then, I found in my stash, yet another sender, a dirty, rusty looking thing, dunno where I got it from. Fitted it and, sweet! I works spot on.
Sorry I can't offer advice as to what was wrong with the original sender unit, I haven't needed to investigate further...if it ain't broke, don't fix it!! If you can find another sender unit, try it, may just work....good luck.