I had this situation on an old Aerokits Crash Tender that I restored. Though there was no motor with it and the hull was in a very poor state I noticed the stern tube was plain steel with no evidence of bearings though the prop shaft was a good fit.
I got round this by lubricating the shaft with Marine Grease (Dynamite Marine) which is a blue grease that I use on my fast electrics. This can be purchased from Wheelspin Models. You can also purchase a grease gun from them which is very useful as you can fill the whole stern tube .
On my fast electrics the flexi drive to the prop is in a nylon sleeve that is flexible but does not have bearings installed. As the brushless motor exceeds 22,000 rpm I can confirm that the grease does a good job as I have not had a failure with it.