190k, needs new wiring harness & head gasket, crank seal(I assume it's the front seal). If it were me I'd fix it. If you like the car so much, just fix it. Take the opportunity to renew the cylinder head while it's off(new valve guides & seals, seats recut, valves ground, lifters, etc) and you just might discover you've got a new car. Any MB with no rust or body damage is worth the cost of fixing.
On trade-in it will be worth almost nothing. Even a car that's well-sorted will return a pauper's pittance at the dealer. Then that dealer will band-aid it up somehow and sell it for three times the value he gave you for it. That's how used car profiteering works. If you want some dealer scumbag to profit at your expense then go for the trade-in, and suffer accordingly. Keep the car, fix the issues, and be happier for it. If there was any car worth the trouble of sorting out it is a Mercedes-Benz w124 E320 wagon. This car is NOT a throwaway. Can't believe you can't 'justify' fixing it.
Selling it for parts would be sad, and take forever.

__________________
'02 BMW 325i
'85 300D 450k
'93 190E 2.6 170k(killed by tree)
'08 Ducati Hypermotard 1100S 6k
'06 Ducati S2R800 14k(sold)