Charge the tyre with air conditioning fluid then use a sniffer or an ultraviolet light. See

http://www.justoffbase.co.uk/Air-Conditioning-Leak-Detection-Kit-Sealey-VS600

also see Adixen.co.uk maybe for some ideas.

Normal engineering crack detection techniques, so called

- dye penetrant

or

- ultrasonic scanning

around the rim.


I know it is very hard to fine small leaks. There was man on Ebay selling a wheel that was replaced by the MB dealer. He/they eventually found the crack in the rim; welded it and was selling the wheel.