Never put oil on mine, ran it for hours and hours...no problems, overheating, slipping...nothing.
Just works and works great.
That being said, I was lucky.
Also got an HF pinpointer that had to be adjusted almost immediately, and the switch went bad in about 2 hours.
I am handy, and repaired and adjusted it and it was fine from then on.
I was in retail and have much experience with products from factories in Taiwan and eventually, China.
Quality control are not words a lot of these places understand.
New workers coming and going all the time, and it takes time for them to be trained to do their job correctly...every time.
A large possibility that yours was just not set up right from the beginning.
Tension on the belt would be the first thing I would check.
Not enough, the drum will slip.
They might test these to see if the drum turns before shipping, (maybe), but not under any load, so they would not have caught this if that is the case.
Here is what it is like inside one of these.
On this one, looks like a few nuts hold the motor in place, loosen them up, move the motor back a bit, then go a tumblin'!
Newer models might be different, slightly, but I am sure the motor adjustment can't be difficult on these, either.
www.youtube.com/watch?v=h5V1Yij4H5k