general problems of the 2002 Mercedes Benz C Class

In October of 2001, I purchased a new (2002) Mercedes Benz c-240. It came equipped with german made continental contouring tires. It is with these tires that I am experiencing a problem. I have 19,000 miles on the car and already have had two slow leaks in two different tires (passenger side front/rear). The first tire leaked (at about 17,000 miles) but able to be patched. When I brought the second tire into an sts tire dealer, I noticed that they sold continental tires. Since I had the two problems, I asked the manager if they sold many continental tires and explained my experiences (in both cases the tires had nails, or similar metal, embedded in their tread). Again, in the first instance, the tire was repaired. In the second instance, the damage was too close to the shoulder of the tire and could not be properly patched. I had to purchase a new tire. Here is my concern. The sts manager, asked me if my tires were factory tires. I indicated that they were the ones that came with the (new) car. He indicated that factory tires are typically made to the specification of the auto manufacturer, not the tire manufacturer. He explained that because the auto maker orders tires in such quantity, they can set their price. In most cases, for the tire manufacturer to be able to meet that price, they need to adjust the composite formula of the tire -- essentially manufacturing inferior tires. This was his explanation of why I might be experiencing problems with my factory tires. He further indicated that tires sold to tire retailers are manufactured to the tire makers' standards and will provide a much longer useful life (he indicated 60,000 + thousand miles for the continental contouring tire I just purchased to replace my original equipment tire). The kicker is that continental does not warranty their tires against road hazards! if his explanation about factory tires is true, this is very disturbing and I believe that consumers have a right to know.