Oil change - will this cause issues?

[PaulSmith]

I would always do a double change on a second hand bike. For a bike in the condition you described, I would keep changing the oil every few hundred miles until it came out clean, and only then, put the good stuff in. It is not really the distance between changes that matters so much as the heat cycles. Get it up to temperature a few times so the fresh oil can melt and dissolve the built up gunk.