Wow these have really jumped in price
https://www.modelsport.co.uk/product/spektrum-sr215-2-channel-dsmr-sport-receiver-437376
the 2ch was £26 and the 3 ch was cheaper than link above
I guess you wont be going spekky now
We tend to use a red sticky bicycle grease in our crawlers but dont see any reason not to use lithium grease
dif oil will probably leak out as they may not be sealed
Grease also helps stop water ingress