By way of apology to Guardian:

Since I had some fun at Guardian's expense recently, when I saw this one in the quarter boxes, I had to pick it up. I think I might've had it when it came out in 1988 as well, but I'm not positive: Superman #27, "Of course you know, this means war!" Written by Roger Stern, pencils by Kerry Gammill, inks by Brett Breeding.

This issue is from before the Superman titles had triangle numbers, indicating what order Adventures of Superman, Action Comics, and Superman should be read in, but it does have an Invasion Aftermath Extra triangle. Previously in the main Invasion book and his own titles, Superman had been roughed up a bit by the Daxamites, the Thanagarians, and at one point was fished out of the river by Guardian and the Newsboy Legion. After helping out with a crashed alien ship in Australia, the exhausted Supes gets back to the Daily Planet, where a disheveled Clark turns in the story. White orders the front page replated, but also sends the obviously beat Clark home. His apartment trashed in a previous issue, Supes shaves, then falls asleep in front of the TV.

Shortly thereafter, Lex Luthor is having a meeting with Pentagon officials about salvaging alien technology, when the meeting is crashed by Gangbuster. Although at this point Lex was still hiding behind the facade of benevolent big-businessman, Gangbuster knows he's dirty, and is more than willing to cross a few lines to get at him. Luthor is rarely unprepared, however: this time, his secret weapon is Brainiac, which is a little less impressive since this is paunchy carnival Brainiac, but still.

Brainiac begins taking Gangbuster's mind apart, but Gangbuster's mind surprisingly is too strong for him, and Brainy goes down. Disoriented, GB flees out a ninety-story window, making a spectacular, and impossible, escape. Luthor hides Brainiac back in the closet he was keeping him in.

While running across rooftops, Gangbuster bumps into Guardian, who is happy to see him, but thinks GB might be going a bit too far. Gangbuster doesn't want to hear it, and slugs Guardian, much faster and harder than Guardian had expected. Guardian sticks it out, though, and later the enraged Gangbuster charges and sends them both off the roof; Guardian able to catch a ledge, Gangbuster falling seven-stories headfirst into a dumpster. Which he walks away from. Pissed. Obviously outmatched, Guardian still doesn't quit:

Gangbuster's costume tears, revealing...to be continued in Adventures of Superman #450! Yes, I'm not spoiling a twenty-two year old comic! And what are you gonna do about it? What? Google? Oh.

At any rate, Guardian seems very Captain America-like in this one; and this issue is thankfully devoid of the Newsboy Legion. It also doesn't mention any of his clone-business, Cadmus, or other baggage; which is probably just as well. I also don't remember how the big reveal that came out of this went over, since I know I was reading the Superman books on-and-off at the time.