That indicates already that either the airpump is defective or the latch at the trunk ,either way its a headache to fix , not much the latch but fiddling with the airpumps connections when you don't know how to ,seller should have mentioned it to you .
What you realy should do is run away from this car & fast BUT on the other note , the faults it has like you mentioned here are not that bad to fix ,the only one that would concern me the most is to find out exactly where the oil is coming from on the top of the engine ,if it is only the cap that is leaking (unlikely but possible) ,then you might like to look a little more into this car .
Test drive it & make sure you run it hot ,engine operating temp with ac on etc ,90c ,look behind you for smoke etc gears have to change smooth ,you know what I mean ,all the rest can be fixed with some of your own handy work in the garage ,including the worn out seat .
It does sound to me that this car is in need for the upper engine harness ,you can purchase them on ebay ,sometimes they are there ,check the harnesses on that car for cracked insulation on the wires all over ,priority # 1 .
PPI inspections are an excellent choice but you have to get & make sure it is a mechanic inspector that knows this specific model (W140 -V12) well enough that he would know where & what to look for in regards of the typical faults these cars have ,not even a Mercedes mechanic knows what to look for these days on a w140 ,remember that ,all they want from you is the money for the inspection nothing more & then tell you some crap that you probably already know anyway .:thumbsup:
Like Stryker above mentioned ,6K could be a bargain over there were you are at ,offer him $4000-3.500 ,this way you laughing but look into the oil leak 1st .