Rather than Helicoil , which are very good without doubt , try the following
https://eshop.wurth.co.uk/Product-ca...SNDYh63vITVEv9
They create a stronger mechanical repair , Mercedes cdi engine have this issue & these inserts are a far more effective method of repair . Before any one leaps on my back about helicoil repairs , it is using the right tool for the job