Jerome wrote a review of MSR MiniWorks/WaterWorks Maintenance Kit on March 19, 2009
The kit is straight forward replacement parts for the water filter. It contains the 'O' rings for the filter. What the kit does not contain is the umbrella valve for the 'Mini Works' filter. I called MSR about the missing valve. The reason the valve is not in the kit is because the umbrella valve is not replaced very often. This is a good thing! Although, I did call and was sent the valve just in case if it were to go bad in the backcountry.
I have had my filter for 5 years and use it occasionally. No complaints. Keep the 'O' rings well greased to ensure proper seal.
The kit is a must have in order to maintain your filter. If you spend the money for the filter you might as well buy the kit. You'll need it sooner or later. to quote a movie 'It's better to have it and not need it, then to need it and not have it.' This is for you WATER!
You don't need any filter if you don't mind boiling all your water. How fun would that be going hiking and stopping every few hours to boil water?