I have owned an 89 300CE for 18 mos. Bought it because it is the best looking car on the road. Now has 166K. Just returned from a 600 mi jaunt and report good news, ran strong and fast. You know you will have some issues and some repairs, but "What price beauty?"

Right side oil leak is typical, but may signal a head gasket problem. I'd spend the $ for compression/leakdown test. Then at least you'd know.

I didn't see any A/C work done. You can expect some.

Brake fluid black? Calipers are not that much $ for these cars and rebuilts are available. Safety first. If owner ignored the brake fluid, might also have neglected the coolant. Nothing like a good flush and the right golden coolant to help with the temp problems.

I don't think you'd offend the sellers if you just told them what you would be willing to pay. If they say "no", then you give them your # and wish them well. How else will they get an accurate idea of their car's worth?

I paid $5k for mine, 150k mi, full service records, incl orig invoice, the guy paid $59K for the car in 1989.

Looks like if you buy it right and spend some $ to get it right, you can have a great car for $6 or 7. That's a good deal.
goodluck