Yea well....your right....but I'd prefer to keep my oil non-sparkly😅

]   Don't worry, the gears will grind the circlips into dust in no time.

I don't see how the axles could come out either.....I was more concerned about the unknowns surrounding whether or not the circlips have seated in properly.....or if they have broken or had been pushed through into the centre of the diff ready to go for a ride through the gears.

Dealer techs aren't going to be the greatest source of what is normal, usually, because as you highlighted, 99% of the cars they see are the "ordinary" ones, whereas obviously a place like ClubSub or some niche Subaru guy is going to have a concentration of "weird" Subarus.   As you have clearly discovered there's a pretty enormous list of possible variations of axle+diff centre+diff housing, each possibly having a unique configuration.   Don't overthink this one. If you can think of a way your rear axles could come out during normal operation without there first being a catastrophic failure of some suspension component I'm all ears.

Just thought I'd let you guys know that I have been in touch with 4 Subaru dealer technicians, two qualified mechanics and the Subaru tuning specialist to tunes my car. I have got a variety of different responses, the mechanics think the clips should NOT be left in the diff...the dealership technicians have contradicting opinions, some say they should be left in the diff, some say they shouldn't and one guy reckoned there shouldn't be any at all!?. The Subaru specialist was absolutely adament that the clips are supposed to be left in there (on a R180)  and he had many colourful things to say about the dealership technicians as he thinks they should know better.   Another thing I learnt is that the front axles ALWAYS has clips that come out the "normal" traditional way.   My research told me that there are varying different varieties of Subaru diffs that use both methods (clips staying in is a bit rare and niche though I believe), therefore I decided that because they were both left in the diff it is more likely to be by design than by something going wrong....and the tuning workshop guy really convinced me as he deals with the older performance Subarus opposed to the dealership mostly doing new stuff.....and the qualified mechanics wouldn't be super familiar with niche Subaru things in particular.   So I popped them back in with a tap of the heavy hammer....applied some pressure with a prybar to confirm they were locked in....they were......then I pulled them out and looked at the circlips to make sure they were still in the same position as I first saw them and hadn't sheared off or broken......I put them back in and repeated about 3 times until I felt comfortable about them.    I haven't put oil back in or driven it yet ....but if anything goes wrong I'll be sure to post about it here!       Also when I pryed to make sure they were locked in I noticed there was a bit of side to side play in axel when applying pressure to confirm the axles were locked into the diff.....probably about 2 or 3mm of movement? Is this normal? It made me a bit uneasy as I don't understand how it can have play if the circlips have locked it into the grooves? None the less the axles required quite a lot of pressure to pop them out so I assume they are locked in properly?   Has anyone got an opinion about this?           many thanks to all..... I'll be sure to let you know when I have a whining rear end and grey pastey, sparkly diff oil 😅