My 10 plate 500 has failed its mot on front suspension top mounts. I think the rubber has degraded and in consequence the top mount has deformed.

Can the rubber mount be replaced in situ or do I have to removing the whole strut ?

A windy gun.on a socket will whizz off the nut

Then you can swap the discs over and whizz the nut back down

Keep the wheels on the ground.. then nothing will move..

So a 5 minute job

Read the GUIDE

https://www.fiatforum.com/500-guides/440891-front-shock-absorber-replacement.html?p=4363637

The strut top has a hex socket in the end. I used a socket set hex key to hold that and a deep offset ring spanner on the nut (17 or 19mm IIRC). It's not horrendously tight and came off easily enough. Just be careful not to get confused which direction they each need to go.

If the rubber has perished, with the car on axle stands, jack up the wheel and fit spring compressors. Lowering the wheel will give ample room to work. Alternatively, you can use a pair of ratchet tie-down straps to hold the spring in compression. This allows you to remove the top mount, replace the bump stop and gaiter as necessary and refit the top nut.

When done, jack up the wheel (again) and slacken the ratchets.

EDIT -
The top bearing is supplied with minimal grease. If the bearing will separate easily (some will some wont), it does no harm to pack to the brim with moly grease. It does not rotate so it wont get overheated like an overfilled wheel bearing. The extra grease helps to avoid the rollers rubbing themselves into dry spots that rapidly wear.