Toilet fun, not.

At the back of a toilet there is a rubber ring to seal the sewer to prevent unwholesome fumes from entering your nose. And no, rubber does not last. After 20 years, or less if you bought rubbish, the ring cracks. (The cut is mine.) And yes, it leaks. Luckily engineer Jansen spotted it quickly, and no damage was done.

What you do normally is detach your loo by unscrewing the bolts it is bolted to the floor with, shift the toilet forward, put on new ring, put toilet backward, screw tight bolts. Unless you had moronic previous owners who cemented the toilet to the floor, ansteystyle, and there are no bolts.

So, can't move the toilet, can't put on new ring. Resorting to silicone. Stuffed some nylon rope in the gap, and filled it up with nice flexible silicone, so posterity can replace that in 20 years.