grammar things - help please

I've got a silly problem... I used something like this in a sentence "siuda was always much of a help for me". Someone is arguing with me, that using "a" before help is a mistake... I thought I was right, but I can't explain it... Am I right here and if so, why?

'much of a help' is perfectly correct

looks encouraging, but I need a strong, grammar based proof on that one... If it's correct (which I still think it is), then why is it correct? What grammar rules make it correct? Or any rule whatsoever...

tak trochę na około tłumacząc:

po 'much' nie można użyć 'of' jeśli stoi tam bezpośrednio rzeczownik.
Jeżeli użyjemy "much OF' trzeba następnie użyć jakiego determiner (this/ my/ a, etc......)