Ah, I remember when Zucker changed out of his shirt I was so mad! Instead of buying a bunch of shirts there's a way to guarantee changing him into his shirt but it might take a few tries. You only really need two flan shirts. 1 to change him, and a backup just in case he ever changes out of his shirt again. All you need to do is write a letter with the flan shirt attached to it. DO NOT send the letter in the mail, keep it in your inventory and save the game. Time travel to 4:57p.m. and send the letter before 5p.m. Mail goes out at 5p.m. so that means Zucker will receive it. When it's past 5p.m. try to find him and see if he's wearing the shirt. If he isn't reset your game and time travel back right before 5p.m. and repeat the process until you see him wearing it. If he is wearing the shirt make sure, save your game! It might take 5 tries or so if you're unlucky, but you won't have to waste shirts and his house won't be cluttered with a bunch of flan shirts. I hope this helps!