shower that won't turn off - and replacement parts

[deewillow]

I have a newteam 3000t shower which is about 7 years old. Its recently developed a drip, that has now turned into a more persistent flow of water that you cannot turn off. A 'DIY handy' friend suggested replacing the Pump Gland O ring. I've tried the manufacturer (now owned by Bristan) and this shower is no longer made and they don't have any spare parts. Does anyone have any suggestions before I have to think about replacing an otherwise ok shower. Do these 'rings' come in certain sizes maybe and I can get one from somewhere else?
Apologies if these are daft questions!!!

[htg engineer]

If its just an O ring that has split or deteriorated then you should be able to find a O ring the same size. Take the O ring out and go to any heating / plumbing shop and they should have one.

Some showers (most new ones) have a pressure relief valve that opens if too much pressure builds up in the shower,

where is the water coming from, the shower head or the bottom of the shower unit.

[deewillow]

thanks for the reply.....the water is dripping from the showerhead - so at least its not leaking from somewhere it shouldn't!!
I'll see if replacing the O ring helps..