Yeah, it's the same with the DX Batman. Some have the abdominal leakage while others are fine. Luck of the draw, I guess. I can't complain though because this is an older figure now.
Well the Batmans are different, for one, I think they've all now leaked, but also, that was a defect from production.
This Rambo figure, I've read stories like this one where over time it's broken down on some people, but there's got to be something environmental to it, if the rubber were faulty, I would think they'd all break down, but everyone's displays and storage are under different conditions so it seems natural that varying levels of heat, moisture, etc. will be present and some will cause breakdowns and others it'll be fine.
I don't generally worry about HT rubber figure longevity because I've got cheap rubber toys from childhood that are as fine today as the day I got them, over a decade old, and in theory, HT should be working with stuff that can last equally long, at their prices there's no excuse if a $20 toy can outlast their products.