Just to clarify:
* are the PCs besieging the castle? Or defending? I'm guessing the former because you mention "dungeon crawl".
* is "Castle Siege" a different game or something? Or just a genre? I ask because you capitalised it.
For defending a castle siege, B10: Night's Dark Terror (basic D&D, or 0e) has a sort of castle/compound thing that the PCs defend from hordes of goblins. Lots. Of. Goblins. Also WGM1: Border Patrol (1e, Greyhawk) has a nightly siege of a fort in it.
For PCs besieging a castle with lots of dungeon crawling, too, there is always A2: Secret of the Slaver's Stockade (1e), though besieging isn't really what they do - they find a secret entrance and sneak in Trojan style. But the compound reacts as if under siege and they may have lots of problems if they're not careful.
There are probably many more (it's a classic theme) and I'll peruse my collection for ya.
