Beware of heat cured materials.
PVC is quoted as having a glass transition temperature of between 60 - 82degC, while that Fimo clay is cured at 110degC. I had to repeatedly remind people I worked with that the PLA (glass transition temp 60degC) was not suitable for prototype tooling that would see 110C process temperatures. Finally having to prove the point practically...we were left with a solid puddle of what was once PLA tooling that looked like what happens to cheddar cheese under the grill!
Another thing is that many "hard" epoxies are also rather brittle, something which PVC is certainly not!
Finally, it matters not how strong or hard the repair material is if it does not form an equally strong bond with the PVC. I could not count the number of plastic repairs I have tried, or seen, where they failed at the interface with the base material. PVC and ABS are easier to glue than many other plastics, but still needs to be considered.
I think that my personal choice might be this stuff: Devcon Plastic Welder.
Plastic Welder™ White is a tough structural adhesive Suitable for ABS PVC, SMC, composites polyesters, polycarbonate, strenics, PET, fiberglass wood, concrete, ceramic & metal.
itwperformancepolymers.com
It is available in the UK, Axminster has it, as does Sussex Model and Amazon. It has a very similar hardness to PVC (compare them on the Shore D scale).
Long ago, someone kicked my Honda's wing mirror off, broke the bracket. I used that Devcon to reattach and it held for a couple years, until I decided to spend the £90 and fit a new mirror.