To makes matters a worse, the case was open (side access panel removed), as it had been running a little hot and I was going to check its fans, with the possibilitiy of repositioning them to see if that made any difference.
Anyway... I froze as soon as I realised what I'd done (my usual and somewhat unfortunate reaction to something "bad" happening). Luckily, there wasn't much tea to spill, and it landed on top of the case and just beside it, with none appearing to have splashed inside. A few paper towels later, and all is dry once more.
I've previously ruined a keyboard or two with spilled tea... only too easy when engrossed in thinking about something, and then absently reach for it without looking! Maybe I should pay more attention to the world around me. :-)