I have a LA1002 FEL on a M4900 that started leaking at the up/down control valve. Is there someone out there that can give me some tips on how to go about checking the valve. I suspect it may be the o-ring, but not sure. I removed the two allen screws holding the collar down over the o-ring, lifted the collar and inspected the o-ring in its normal position surrounding the "plunger". It seemed to be o.k.; however I did not disassemble the valve. Wasn't sure how to proceed and thought I would ask if someone could give me step by step instructions so that I do not take a wrong turn. Thanks.