Aluminum Flue Pipe Corrosion / Poor boiler flame correlation?

I noticed this flue is staining the shingles with apparent oxidation of aluminum. At closer glance, the wind cap is corroding on the down-wind side. I checked the flame on the boiler and find it too orange. There is a lot of sediment in the burn chamber. Is this an incomplete burn causing a sulfuric condition leading to oxidation of the aluminum?

Morning, Paul. Hope this post finds you well.
Is the residence near the ocean?

Appears to be sheet metal pitting.
May take on this is corrosion from condensing flue gases. Salts in the condensate.

How old is the boiler? Serial/Model number please.

You state the flue is aluminum. Any markings on the flue?

Lets await what others have to say.

Thanks for your response,

This one is in Colorado.

There is no Serial number tag to be found. Home owner says the boiler is original from build date of 2004, 16 years. It is a Laars Mini-Therm.

Type B vents are usually made with an aluminum liner and either Galvanized steel or stainless steel on the outside. Yours looks like Galvanized on the outside. IMO the galvanized coating is deteriorating and staining the roof.

Rust and pitting : While rust is not as likely on a stainless steel chimney, corrosion can occur because of the corrosives in flue gases and in moisture that may develop inside of a chimney.
Interesting read.
Observation: Galvanized Flue pipe. Pitting, corrosion, meal oxidization, erosion, damage, material ware, material/galvanized steel gauge loss and damage.
Recommendations: Recommend a licensed gas fuel boiler installation and repair contractor: 1: Replace the flue. 2: Evaluate and Service the Laars Mini-Therm boiler prior the next heating cycle.
Act Upon Any Recommendations Prescribed.
Limitations: Warm weather. Prevents observing in heating mood. Boiler not in operations. Boiler pump not tested. Heat loss calculations. Not done as part of; not applicable to; the severe agreement. Data plate on equipment; Not located/Not found. Ect, Etc, Etc.