@M8.8 I don't know about using it with the Mana board but you can certainly use an offline controller, I do with my CNC and T2Laser. It has a different brand controller, but very similar to the Mana and all this controller does is send serial commands so should work if you wire it correctly.
You can use International Rectifier IRLR7843 (HEXFET Power MOSFET). I would strongly recomment attaching a heatsink to the mosfet.
I had the same problem as you on my board (arrived faulty) and replaced it with mosfet above. I would strongly recommend attaching a decent heatsink to the mosfet.
Given that the design of the board is weak with no overcurrent protection, no soft start etc. I have decided not to use the board for the spindle motor other than for very light tasks. As most tasks require you to set a speed once I decided to attach an off board speed controller with manual speed control and some protection built in.