You also stated that you use it in your yard. Might be hard to beleive but grass put a huge amount of stress on the electronics. Also the RPM's are a touch on the high side for a truggy, IMO you should have about 2000kv on 4s. My suggestion is to def bite the bullet on the motor. Spend a little more and buy a Medusa or the CC/neu from Mike $140 or less depending on what you choose. The MM should still be fine but don't keep trying to use it with that motor!
Sorry, never know these days, week and a half ago all the snow here was almost gone, a week ago we got a foot, now it's just about gone again. Snow can impose a lot of load too though, esspecially if it is slushy and sticks to the tires and chassis. Either way my bet is your motor is toast and you should upgrade to a quality motor now.