My 2005 Roadster doesn't ever cancel and I consider it quite dangerous: it's hard to switch mindset from a modern car and remember to manually turn it off every time you use it. Worst is when the left indicator stays on and the person entering your road thinks you are turning left: only thing that has prevented an accident is that incomers are so busy taking in the car that they assume you are weird which is confirmed as you sail past! A simple solution might be to wire a more prominent flashing light into the existing one and place it somewhere central.. maybe a police light would do it! There's 12v going to the existing invisible flashing light, so it shouldn't be hard to extend that with either audio or visual.. LED would be tiny voltage so shouldn't upset the system..
Oliver S.