Persistent exhaust leak, BMS Heritage 150, GY6

[Roscoe]

Yes, one tooth off on cam timing will cause problems. Here ya go ... https://www.buggydepot.com/tech-cent...ad-center-tdc/
When you get the new exhaust, make sure the exhaust pipe flange to the head is parallel when the whole assembly is hanging in place on all the brackets. You'll be able to slightly bend a new pipe, once it's been through some heat/cool cycles the pipe will be much harder to bend. When it matches up as designed the exhaust should last a long long long time, Check those exhaust bolts frequently till you are satisfied they are staying tight. If you can get the scooter up waist high when working on the exhaust it makes the job a lot easier.