I have been getting the common pulsing with this pump (UV0814) so I stripped it down to give it a clean. I found the top compartment that houses the microswitch was soaking which would also explain why the pump was beginning to be intermittent. However as I was re-assembling it, I found an O ring about 10mm diameter. Looking at a poor quality exploded diagram on the net, it looks like it fits between the top of the grey diaphragm and the upper housing. Has anyone stripped one of these and can you confirm this is where the O ring goes? If anyone also has a diagram I would be grateful if you could attach it to your reply.