XRAY - Model racing cars

Hey Guy’s

Just a quick question I have a NT1 ‘08’.
The car is great to drive having heaps of fun with it only still learning how to drive it.
I have put around 2ltr of fuel through it. But so far I have replaced the left hand side front diff bearing (941016) due to it melting the composite adjuster ball-bearing hub (332070)
And last night at racing the front left hand side inner (941016) wheel bearing I found half way through the race the car was not right.
We stopped the car and found that the left side wheel was not right we removed the wheel and found the composite steering block was starting to melt due to the bearing locking up.
Is this a common thing with the NT!?
Are the standard bearings out of the kit dry bearing or filled with oil?
Can you get a set of bearings that are filled with grease? Or is it worthwhile to remove the bearing shield and fill with a light bearing grease. Yes I have seen ceramic bearing but they are a little expensive.
Does Xray have a grease to suit the bearings in the NT1 kit?
Do you guys have this problem with the bearing?
How do you guy’s maintain your bearings?Or do you guys have any ideas?

Thank you

XRAY suggests to use the for servicing.

Thank you very much for your help guys