1979 450SL worth less than others?

Hello, 
While looking at Hagerty's r107 value guides, I noticed the 1979 450SL is worth less than the average 1978 or earlier. Was something changed on these models that was problematic? I know the AC on the 1979 models isn't that reliable, but is there anything else I'm unaware about? Would a $6000 white on blue 1979 450SL with 130,000 miles and no rust, that needs a new soft top, has a cracked dash, and a small paint chip be a mistake to purchase? I've heard the most expensive thing you can buy is a cheap Mercedes... 
Thanks