I've seen worse. I ran into a guy with a euro 240 that got an aux tank installed, because his tank would only hold... 6 gallons...!!! it was nigh flat. he thought it was because of the wrong fuel cap, and I explained to him about the bell behind the car... he'd drilled a hole in his filler cap to keep it from happening.
the amazing thing is it only takes about 8" vacuum to collapse the tank... and about 3 or 4 psi to refill it.
I've put the cap on, plugged the fuel line, and blew with shop air, and popped the tank back to nearly perfect shape. but the creases are always there, and I think they will rust. a tank swap is best.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!