回複：but....

There are a lot of posts on MB forums on oil discussions, but never come to a real conclusion...

it is believed that 95% of engine wear are contributed by cold start. Syn oil has a character of free liquidation in low and high temperature. When I switched to syn oil, it is noticeable in morning that engine runs much smoother from the first turn. I was convinced from that. I also read actual posts from user oil analysis, it appeared the results showing positive effects of using syn oil over extended oil change intervals. Some people change filter between oil changes, I think for 7500mi a single filter is fine (my Jetta TDI requires 10kmi oil and filter change specified on manual).

Cost-wise, including oil and filter, it's about the same between convention and syn oil, or syn oil is slightly higher, but marginal in my case. The real benefit is the protection of wear. Particularly in Canada I think it'll make difference.