Fixing a rear 3/4 panel

Saw a Golf today, but there was excessive bubbling on the rear 3/4 panel on the drivers side. Guessing the washer bottle leaked and water has got into the panel.

How much for a new panel, to paint and fit?

Or can it be repaired?

Rust on bumper mount means the mount has bent out of position.

S

Hard to say exactly without seeing where in particular the panel is corroded. Quite likely the root of the rust is from the arches and has found its way up into the rear quarter. The rear arch and filler neck panel are available as panels. Hard to say how much someone would charge to sort this?

Where exactly is it rusty ?  As Markwon said, it's probably due to crud in the arches. Settles on filler neck and rusts neck and rear quarter around the filler cap (and inner arch) - repair panel for quarter available. The seam between inner and outer wheel arches rusts and allows water to drip down and rust out the bottom of the quarter panel above the sill - again, new rear arch panel and/or sill should cover the area. Also rots along seam where rear panel is welded to quarter panel, but should be easy enough to repair. Never seen rust in any other areas than these. Finding a complete quarter panel will be quite a job nowadays (ie, expensive !). Fitting a complete quarter is a big job. Guessing here but I'd expect to pay about ?150 plus for the panel (if you can find one as obsolete), and ?500 plus to fit and paint ???????? Whoever fits it would prob end up replacing the inner arch, etc, due to rot, so could well be more.