My '01 XC 200 seized like yours . It turned out to be a bad left (or mag)side crank bearing. The cage for the ball bearings came apart and wedged between the crank & the cases.
It's a pretty easy & straightforward engine to work on, imo. Also, if you do a search on this forum, there's a very good step by step engine rebuild report posted. It's for a 250, I believe, but , except for using a different right side crank bearing, the same as your 200. I used it when going thru my 200. It was a great help.
Or, pull the engine and take it to Neels .
One other point. My GG owners manual says to use syn oil with prem. fuel at 50;1. That's what I use and it has worked fine.
RB