Devised by Brainiac 5 and presumably based on the experimental Serum XY-4 (Adventure 300), the anti-lead serum protects Daxamites from lead poisoning and allows them to use their powers under a red sun. The raw materials are so scarce that only one dose can be produced every 48 hours. Curiously, Mon-El takes his serum every 8 hours; logically, he should run out after the first dose. This discrepancy remains unexplained.
One of the rare ingredients of the anti-lead serum is kryptonite.
Beginning in Adventure 350, the Legion finally found a servicable replacement for its aging fleet of Mark 03s. The Mark 06, obviously based on its predecessor, served the Legion well until Adventure 365.
At least six Mark 06s were seen in service: 3 red, 2 yellow, and 1 blue. Others may have been in action behind the scenes.
With the advent of the Mark 10 cruiser, the Legion finally had a state-of-the-art fleet that was a worthy successor to the Mark 03/Mark 06 design. Fully equipped, spacious, and striking in design, the Mark 10 served the Legion from Superboy 184 thru LSH (v. 2) 285. It was replaced by the Mark 494.
The Mark 11 cruiser replaced the Mark 494 in LSH (v. 2) 303. More compact and more heavily-shielded than the Mark 10 or Mark 494, the Mark 11's modular design facilitates mass production, allowing for easy repair and replacement of damaged vessels. As hard as the Legion is on its cruisers, this is a definite bonus!