You can do just the driver like Marc said to completely make it a mp40wqd you need to buy the new wet side also it has been redesigned also here is a quote on the different upgrades
"Upgrade to the new QD driver, resulting in reduced noise and increased efficiency
Upgrade to the QD wet-side propeller, resulting in increased durability
Upgrade both the QD driver and QD wet-side propeller, resulting in reduced noise, increased efficiency, and increased durability."
If your wet side needs to be replaced or its old I would buy a wet side also along with a driver
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