PCL Mk2 airline

[Smiley]

I have an old PCL Mk2 airline gauge - had it for years and it wasn't new when I got it. It's a proper old fashioned bit of "made in England" engineering. But today it has started leaking air at high pressure from the top nut undler the lever. I've stripped the mechanism and cleaned it out but no luck. Does anyone have a parts diagram or any info to suggest what may be wrong? Yes I could buy a new one but I like the old one.