I'm trying to run again to get the WR but can't manage to find a consistent way to get the triple 7. Does anyone have a trick or something ?

At the start of the room, the 4th slot machine cycle is a triple 7. In runs I would always try to catch this cycle by waiting for the right moment (had the timing pretty much internalized), then mashing. Your first hit can even be one cycle earlier, since that cycle has a 7 in the leftmost column. As a backup, if you don't hit the right row, but get a perfect mash (such that you didn't desync the columns), you can try for that triple 7 row again. I never had any strategies besides this and winging it, although if you're aiming for WR, you'll probably reset after missing once, anyway.