He is not scaming you but you may be able to get some relief from Lennox. there was a serious problem and recall on some of their furnaces I've attached a link which will show you some info.
hope this helps
Please accept and positive feedback is appreciated
If you read through the link that I sent YOU TOO will see the mention of PRESURE TESTING Lennox heat exchangers. If you read and follow the links I'm certain you will find it in there.
ToCustomer Because you are not getting CO reading inside you home does not mean there is no hole. But at what point will the hole get bigger and you will. It definitely is not going to get smaller.
The furnace is 22 years old and normal life expectancy is 15-20. I think you should bite the bullet and upgrade anyway
Hope this helps