Sitting back proudly thinking how smart I was to do this instead of all those idiots that buy fancy $200 reservoirs, I decided to reinstall the airbox and inlet tubes that had to be removed to get the original reservoir out.
The right side air inlet tube tries to occupy the exact same space as the new radiator cap. All my dealership memories came rushing back of flushing cooling systems on 848s and 1198s. They use the same 999 setup and the fit is so tight you can’t even remove the radiator cap because it hits the underside of the air inlet tube. I had the same problem, only worse because my air tube wouldn’t even fit. At this point, there’s no time to get another 998 style reservoir. I’d also need 998 radiator hoses before the weekend because I’ve cut mine because I’m a dumbass. Time to make this radiator fit.