Winterized 500 today

[Rapier]

Ran the '69 500 dry today and dumped some Rock OIl into the carbs and down the bores. However, noticed this raised section of ali on the exhaust side, near the non-existent mercury switch (maybe they don't have them on the manual shorty?); picked it off like scab, strange, is perhaps a fault in the casting - this is a salt water run motor though.