My maintenance minder just came on with B14. 4 is to change spark plugs and inspect valve clearance. I was wondering if K20 DOHC is what some call, shim-over-bucket design? I also heard that it is harder to adjust these engines compared to the screw type, however shim-over-bucket design keeps specs longer and thus probably require no adjustment at all? I am just debating if I should even spend the money to have a shop open it all up to check at 100k. Can I get by with just replacing the plugs? My driving summary would be around 80 miles on the highway each day and very little city. Ratio would be around 90/10 hwy/city. Always synthetic oil. Redline maybe once every 2 weeks.