[Milwaukee m18 trigger issues]

Anyone having premature problems with variable speed triggers on their Milwaukee cordless tools? My bosses was unfortunately dropped in a puddle, his local supplier wanted to charge a fortune to fix the problem, it's on a 3/4 impact gun, a new one is only $20 more. I take good care of my own tools and am starting to have the same issue. The unit starts to jitter and randomly change its speed then eventually stops working all together. He paid the extra $20 for a new one and it's already showing signs of trouble after around 3 months. I tore the first one apart and bypassed the variable resistor as I could not figure out how to fix where the wipers had worn through it, there is only full speed now though. My question  is, is this due to various kinds of misuse or are there others of you who take good care of their tools finding this ussue also?

 

[hardly any grease in my new DCF899 impact wrench]

I'm struggling to find out what the correct grease is for these, every person I ask says just put this in or just put that in. Anyone here actually fully know the correct grease ?