Tyre weld is an emergency get you home product only, and I right pita to clear out when the real problem needs fixing which it will do anyway. Plus the wheel balance issues as said. It's not an every day product or we would all have it.
This is a common issue though to varying dergrees. The time is never taken to clean the rim by fitters as they are up against it on time and hence cost. So it's rare ime for pressures to stay constant. But for me the proof of it came when I bought a second hand set of wheels and had time to clean the bits of sleared rubber and corrosion off the rim before fitting tyres, the rim was covered. They now hold pressure far better than any other wheels on any car I've owned previously.
I still check them once a week though, where they loose about 1psi a week evenly over each wheel. Other wheels have been all over the place after a short time.
Also her polo had similar slow leak on two wheels, and cleaning the beed sorted it. If you buy tyre weld kern it for emergencies only, as designed.
