Questions about previous service on my 300E

Hi, I just got the service records for my 88 300E (I've had it for about two months) and I have a few questions I was hoping you could help me with. The car has 197,350 miles and the idle is a little rough. The car is fine while under acceleration but come to a stop (after it's warm) and it shakes. The rpms go up and down a bit and the oil pressure drops a bit below 1. Apparently the previous owner (who bought the car with 64,500 miles in 10/93) had this problem before and was never fully resolved. My questions are the following:
1) The last tune-up was done on 12/97 at 162,500 miles. Could the rough idle be helped by a tune-up?
2) On that date the prev. owner took it in for engine noise. The shop wrote on the repair order that there is "a little lifter noise. Early signs of valve job. Blue smoke with rubber smell after car sat for three days." What's involved in a valve job? The car never had the valve job and I don't notice any noise. Should I be worried about that?
3) On 6/98 (170,000) rough idle. A scope test was performed and checked OK. What is that and what can it tell you about the idle.
4) On 8/98 (171,100 miles) the owner took it in because the car was idling rough and would occasionally die. The shop wrote "rust in fuel head. further repair might be necessary." What is that? It was never repaired. Should I have a tech look into it?
Thanks. I'm sorry for the long post but this is my first Benz and I don't know much about them (yet).

[This message has been edited by arias (edited 03-15-2000).]