125-200cc front brake rotor for 1999 wr250 and other questions from a begginer

Hi fellow motonuts. These is my second massage here at cafehusky. I recently bought a used 1999 wr250. Here in my country (Guatemala) the company that sells this brand doesnt carry spare parts prior to 2005 . I need a front brake rotor, the bike came with brembo but its difficult finding the part here. Do anyone know a rotor that will bolt on without any machining? Also I need to change the gearbox oil but im really confused here, i have read in these forum about using semi sinthetic 10w40 car oil or normal sae40 car oil, whats your take on that?
Yesterday I took the day of from the farm and went woods riding, the bike is in great shape. The only thing that was weird is that two times after i couldnt clear a steep section of the trail, I coudnt control the clutch and the bike turned off. It wass hell starting it. I tried for about 5 minutes starting the bike but I cot. I resorted to turning back down anddo a rolling start in second, the bike fired right away. Is it me (a total begginer) or is the bike that hasa problem?

Thanks for all

sorry guys I should have places the thread in the 250 seccion but it dont know how to change it.