I have a question for anyone familiar with this model Fisher MD. I bought this new back in 1990, and believe it or not it still works and looks good. The problem I have is in the battery compartment there is a white threaded plastic ring that the cover screws into securing the cover. Due to age I guess, the threaded ring became brittle and broke. I secure the cover now with velcro strips but have to be careful not to get dirt or debris in the control box. I called Fisher and their rep told me that this part is no longer available. Just my luck. Anyone have any ideas on what I could do or what could be done to fix this? It is still a great relic machine and I use it as a backup. Any help or ideas would be greatly appreciated Thanks in Advance.