I have an E320 of this same year, the engine design is exactly the same - but its 3.2 litres.
a few pointers for Pakistan, ask the owner about maintenance - if you hear terms like "only aail chenj" then automatically assume this car is in the ownership of someone who only cares about "shashka"
the engine is very tough - but a bit noisy - its the nature of the beast - it always has a timing chain type and oil sloshing noise from the timing cover when its old. for oil changes use an oil licensed under the Mercedes Benz 229.3 spec sheet along with oil fleece oil filter from later model and change at 18,000 kms - if you use it on highway the oil change interval can go upto 24,000 kms
It is critical to use the correct oil and make sure the engine gets hot n toasty while running. the secondary air passages can clog in the head if a substandard oil is used and the oil can slugde up if the breather caps on the tappet covers are leaking oil or their pipes are rotten.
This is an old build style of MB - its a hybrid between the W124 and the W140 chassis with a few magnitudes cheaper paint quality compared to the early cars.
the best advice I can give you is to drive this car more and dont pamper it - its built to run and run for extremely long distances.
keep on top of maintenance and use the correct stuff and procedure as specified by benz. Thats the good part about MB - their service literature is thorough and well documented.
as the car is in Pakistan you can expect a few surprises in wiring and also in some mechanical stuff - just sort it out to original spec and you will be ok. remember that if the previous maintenance was neglected in favour of champi paalish of the car and snapping DSLR photos of it then use that as a bargaining medium to adjust the price because you will be paying for all that maintenance - the polish and nice photos wont be good collateral to currency in regards to maintenance.
in absolute realistic terms I can list down the issues that this car has specially in Pakistan, the rear subframe mounts are shot, the rear control arm bushings are torn, the front bushing of the front lower control arms are shot, the main ball joint (aka supporting joint) is shot or loose, the engine mounts are shot (replacement in M112 engine requires unbolting the compressor and alternator), the gear mount is shot too (too much twist from engine) engine is running with water as coolant or el cheapo coolant - which is worthless, the brake rubber pipes are shot, the wheel bearings need servicing, The automatic transmission will be leaking ATF from the connector bushing.
all in all - I have 5 cars under my ownership here, you will be surprised that the one car that is least pulled in for maintenance is the mercedes. It had a few issues when I bought it and once sorted it works like a loyal worker, always ready for any job (including heavy work)