Thanks for the advice all.
So the cleaning made no difference as I'd done this multiple times with alcohol but I did it again regardless.
However, I decided to take a risk. The roller mechanisms have a small LED, which I assume is a sensor to detect when the roller moves. The one which detects horizontal movement was bent back, close to a 45 degree angle unlike the one by the vertical roller, which was standing almost straight up and has no issues with movement. I bent the horizontal sensor closer to an upright position to match the vertical sensor and surprisingly this actually worked, so far the movement in the mouse works great now!
I'm glad to hear that I can use any mousepad with roller mouse, I have not used one in decades and I remember vaguely that the mousepad I used to use back in the day wasn't fabric and had some material on it that the early optical mice hated. In that case, as a precaution and so I can claim my throne as Q3A champion, I shall clean my regular gaming mousepad in preparation for Q3A night tomorrow.
Thanks again! Looking forward to Q3A Friday night!
Online games - Quake 3 Arena, PSOv2, Worms World Party