I purchased a two owner 2014 MX-5 Grand Touring from out of state with only 23000 miles. Just had it in for an oil change and to replace brake fluid. The shop told me and showed me that the Bilstein shocks needed to be replaced - oil and dirt on all 4. Rear tires are starting to cup supposedly from that. Can anyone tell me if Bilsteins should wear out in only 6 years and 23000 miles - unless it was raced?