I have an original Triton combi shower about 10 years old now. Has been a great shower. Has just started to leak. Drip,Drip,Drip when i turn it off. I expect it is like a normal tap and the washer has packed in. Can any one tell me what size washer i need to get and where abouts i need to fit it on the control.Is it called a cartridge O ring as i have found a sight with part numbers on it. The sight is www.shower-spares.co.uk/triton/HP_range.htm. I am OK at DIY but what do you think ? Do i need a plumber to do this job.?