I did a search and found the topic covering Rust on the belly of the Tank and some of the Tank not painted; another item to check. POR-15 stops Rust and needs Rust to adhere. It comes in Grey or Black.
Just above the Slave cylinder I noticed this hollow engine mount bolt and its Brown Nest, what?

I reamed the hole with a piece of Copper tubing and used Black RTV to seal both ends.
While I'm waiting for the new Slave cylinder I'm pulling the Tank.

LOL judging by the rust free condition of the surrounding parts, that's just a mud dauber nest. Hope he's found a new home.

Ive found mild rust on my fuel tank where the seat overlaps. When you wash with water or ride in the rain---remember to take the seat off when you get home. Since I've done that, no more rust.

---

No, it's Rust.

Too bad the fuel Tank wasn't made from Galvanized Steel. Its like owning an old car, always chasing Rust.

what tank is that (was it a tank that was not being used)

Neilp in AUS posted a thread on "Tank Corrosion" on 5/23/13 with many photos.
The water runs around the Tank front and back, get into nooks that are not painted and rust forms. I just used a bottle of Clear Nail Polish covering any and all potential locations.

My Tank looks OK. I still filled exposed seams. The brackets are welded to the Tank and then the whole assembly is painted. The backside of the brackets are bare metal.

No, it's Rust.

That's a first. The tank also has foam padding on it that gets soaked when the bike gets wet. Remove seat after you wash or do a rain ride.

---