My boiler is really old ,gloworm spacesaver 50 bf mk1 , the gas valve has developed a small leak coming out of the main burner nozzle , when in standby, hardly bubbles when you put some liquid on , question is would i get a gas engineer out to change it , if there is a available part , or would i be wasting my time even trying

Yes. gas valves are still available.
It should be a Gassafe fitted part.
If you are competent, then you can DIY. I’d be tempted to get someone in,as the valve may need adjusted when it is tested, which the average DIYer will not be able to do accurately.
I’d pay around £50 to fit the part – get it yourself from a reputable seller.

cheers , after some chacking it turns out by boiler has abspestos in it, so it has to go, any advice on how this needs to be done

Thanks

Step 1) phone a gas safe engineer
step 2) get gas safe engineer to remove your old boiler and fit a new one
step 3) pay gas safe engineer.

Chinnu reckon