hi and welcome, car looks nice - manual too

rear discs can be a bit of a pig to get off if they've worn as a lip is created on the inside by the handbrake shoes - you'll need to adjust the shoes in enough to get the disc off over them ...
whilst you're there, have a look through the breather system cleaning guide - if the oil changes have been extended then they may be clogged up. This eventually results in the cam cover gaskets leaking ... although if they're like the ones on my current omega you might need a few cans of carb cleaner!!!