Anyone done a DIY air conditioning leak test?

As per title, has anyone done a leak test at home on their air conditioning system?

About two months ago, I refilled my air conditioning with one of those Halfords regassing guns, which did a really good job.

The gauge read empty when I refilled it! EEK!

They say you loose approx 15% of gas a year, so I went ahead and filled it up, as it was holding pressure.

Anyway, two months later my air conditioning is back reading almost zero again.

So I have a small leak somewhere.

I have had a good look round all the pipes and connectors and have come to a few suspects, in the system.

I suspect a link pipe to the air con radiator, the radiator itself and perhaps even the low pressure side valve.

It would cost a small fortune to just keep changing components. So I was wondering if anyone had any luck with some of these UV dye based testers? (apparently better than the Freon detectors)

Any advice greatly appreciated.