I don't play MKSC, but I'll still give my opinion on this.
I'm basically a MKDS player, and from what several Japanese players told me, there are rumors saying that the MKDS wifi player "NTTWestJPN" might be the same person than your MKSC "Mander", also known as "Hirano".
The thing is that NTT is also suspected of hacking in MKDS; I must've been the only European to have raced him, and he was able to race amazingly fast on alot of tracks to beat me quite easily, although I think I'm one of the best wifi players, if not the best. In fact, he's the only one to have done that, and he played with an amazing consistancy, only missing when I was pushing him or annoying him. He managed to do several WRs during our races, and remember that wifi races are only done in one try, no 2nd chance. In fact, I had never seen anyone racing so well before him, and I've played all the other top players, even the other Japanese. I also noticed he was able to run faster when behind to catch up easily, plus he was worse on slippy tracks. In fact, I had the feeling he was so confident in his driving that he wouldn't miss anything, and indeed he didn't miss anything. Moreover, there are absolutely no videos of NTTWestJPN racing on wifi (he doesn't play TT; we could also wonder why: is it to be able to hack quietly ?), so the only proofs are his wifi races. And given that I played some hackers without even noticing they were hacking, I guess he could've done so. In fact, I guess the difference could be that if he recorded a wifi race himself, it'd be obvious that he hacks.
Of course, all what I've written stays suppositions. Although I have big doubts about NTT, I can't be 100% sure he hacks. From what I've seen, it's the same with Hirano. I hope that what I added will help you.