any concerns about the rust? it seems to be isolated to the gas line only.
Rust is rust being in the Houston area I would be more concerned about the location of the furnace what kind of humidity is the furnace location dealing with horizontal furnace appears to be in a attic is this correct. Black pipe is going to rust if the humidity is high has no preservative. Where were kitchen and bathroom exhaust being discharged were they into the attic with the furnace. Rust=moisture:D
I would consider air-conditioned air leakage into the furnace burner compartment causing condensation on the gas line.
It’s not just rust on the pipe, it’s dripping.
The usual culprits I find are A/C leakage and humidifier leakage on conventional furnaces and condensation drain leakage on HE furnaces.
Correct the leak, if there is one, … little bit of rust is not an issue IMHO