Atemplar'sfriend22

Hello. I volunteered to perform a tune up/ maintenance service on my friend's 2022 templar X 250 6 speed. i havent been able to locate the chain brand or type that is on it factory. It is on the highway most of the time. I was thinking to keep the 13t and go with a 38t sprocket, any suggestions? also i havent been able to locate the origin of an oil leak that he is having somewhere near the carborator. Is there a common cause that i have missed in the forums? Should i go with the HB20 headlight or an aftermarket led? Thank you for any and all advice!