My semi-built A15 has been running on it's last rebuild for about 8 years now with lots of highway and city miles (lost track). I have driven it very hard and redlined it a lot (~7,700 rpm) in those last 8 years and it still takes them with pleasure, no smoke, oil leaks, knocks, or problems of any kind. I did have to replace the stock valve springs with dual NISMO units, after running the stock ones for about 7 years, but that's all that has worn out. A series are awesome engines for reliability if you rebuild them properly and do a good job with quality parts and quality machine work. It's imperative to have it all balanced too!