Although this thread is ancient, now that I've strip-cleaned my SBLOO, I want to leave a comment just in case someone else has this problem in the future.
The front element is glued in place. Choose your preferred method for making the glue more pliable; I already had some movement in mine, so I just opted for pushing it out (more on that in a mo). As Peter said, soaking the edges in rubbing alcohol/isopropyl should help. Some people suggest applying heat - that sounds like a good way to crack the glass, so I'm not fond of that.
Either way, you've got to get it out once the glue's dealt with. There's some "ribbing" inside the viewfinder's outer shell to stop the glass just dropping out, so you need to push it from behind. In the middle of the viewfinder's foot, there's a tiny grub screw - you'll need a very small 1mm x 0.2mm precision screwdriver to take it out.
Once that's out and the front is loosened, push GENTLY on the rear element using something soft and padded and that should push the front out (so do it over something soft so you don't smash it!). The rear element is glued into the back of an internal spacer; it's unlikely you'll have to remove the rear element to clean inside of it (and it's best you don't, as you could damage and/or rotate the framelines this way), so this should give you easy access to everything you need to clean.
Reassembly is quite straightforward as there's only those two pieces. I opted to try to "liven up" the now-dry original glue/cement with some rubbing alcohol instead of replacing it with more glue as I'd read elsewhere that could work. Whether it has or not I don't know - the "ribbing" might be doing all the work to hold that front element in place, but it doesn't look like it's about to drop out any time soon (fingers crossed). Your mileage may vary.
