Some questions MX5 NA

So, my MX5 NA 90PS Bj.95 has just rushed through the TÜV with timpani and trumpets. The most important points: – At the AU the CO2 value went straight through the ceiling, far away from Gut&Böse. Tips for troubleshooting, there are with the NA any usual suspects (lambda probe, CAT) which are most likely the culprits? Who can diagnose this exactly (repair should not be done in the workshop, AU after repair at the TÜV there included in the inspection fee)? r replacement? – Thresholds in the back, I am one of those who didn’t know that you should check the water drains of the rain channel regularly and break them free. Is there any repair plates for this area or only complete sleepers? The TÜV would already be satisfied with its own statement with a blared sheet metal, but I would prefer to use a fitting piece. Further question that has nothing to do with the TÜV: At ~120tkm(?) the timing belt was changed. a problem (which was probably constructive in this year of construction) which made it necessary to stick on one of the timing belt wheels. The workshop’s former statement: A further change is now unfortunately no longer possible. The car now has 250tkm on the clock, and since it is still possible to bring the thing through the TÜV again I would consider a timing belt change. Workaround to that? Greetings & thank you very much, Toenne