I remember reading about that Ealing Broadway service now. Wasn't it scrapped because of the lack of other units it could couple to in an emergency?
I don't think they would be permitted in the central section of Victoria because of the lack of proper ventilation for diesels but they certainly could visit the Eastern side.
I remember reading on here that a 171 once made it to Haywards Heath in passenger service on diversion because of disruption at Brighton.
The Ealing service was scrapped for that reason, a failed 171 blocking the line with a different coupler to other units would ruin service on the GWML.
Your right about Victoria, the vents are where the thumper exhausts were, different place on the 171. I think the path from Croydon to Victoria was needed by another service too.
Yep, some have ran in service to Haywards Heath, then down to Brighton via Hassocks as well still in service when the line between Lewes and Brighton has been blocked, very rare though.
Some 171s run ECS from London Bridge to Selhurst via Streatham Common to keep up route knowledge in case of diversion too.