Potential rear axle issue?

When buying the 405 I was sure to check that the rear axle wasn't showing any signs of failure, as I know they were a big issue on these models, and was satisfied that it was fine.

However, I was washing the car today and noticed that the rear wheels seem to be a bit too far back and don't sit in the middle of the wheel arch... There is definitely a smaller gap between the tyre and the rear of the arch than there is the front.

Please tell me this isn't a sign my rear axle is finally giving out? It does click from time to time going over bumps in the road, but I had convinced myself that the clicking could just be the struts or maybe even just the exhaust hitting the chassis (deluding myself, I know).

Firstly getting a new axle or axle components will be like finding hens teeth and secondly the MOT expires at the end of May so I'm worried if there is an issue it would cause a failure.

Thankfully although the 405 is our daily driver at the moment (due to the fuel economy), we do have another car so it isn't the end of the world if it does need repairs, I'm more concerned about not physically being able to repair it if parts are obsolete.

Lastly, just to say that it currently has a full tank of diesel and does have quite a lot of crap in the boot weighing it down - it isn't as bad as that when it's less laden and lower on fuel.