Omega Constellation

Crown is not original to the watch, dial looks legit. Rotor bearing may be worn but spares are available. Calculate additional 150-200 GBP for service, but you should be able to recoup that expense at a later sale.

Dial configuration is fine.

Case is slightly soft and the dial has evidence of moisture intrusion from 1-5, most likely through a leaky crown. ( probably hence the replacement)

By the colour variation- Looks like the rotor has already been replaced once but definitely needs sorting again as you mention.

£575 is very cheap for this reference nowadays ( a decent one will likely cost you double in the current market) and they do wear really nicely.

Just depends on how the dial looks in real life.

The one thing you see is the dial- if it is as stained as it looks in these photos you will probably regret buying it, IMO.