What.... nobody is allowed to keep project cars in the yards or on the streets at San Diego?

Just to get the 115 running again, you could unbolt the oil cooler hoses at their source (oil filter mounting?) and plug the holes with short bolts of identical thread. Otherwise regarding your junkyard search - Knowing MB, the 123 oil cooler system should bolt on as replacement with little adaptation. Have heard that Euro 240D model 123's have no oil cooler at all, so it's not exactly a critical part. Only caution is if the 115 oil cooler connects to the injector pump casing somehow which might suffer lack of lubrication if you bypass the OC system.

And if you've got a time limit on this deal and just want to get it home, bungie cording the disconnected PS pump out of the way should enable the car to still be driven... but ask a professional independent MB mechanic first in case i am wrong and internal gearbox components might get damaged, but i dont see how.

Good luck with this revival project. I've seen some amazing success stories along these lines.