1995 Ford Escort Old engine maintainence.

Hi, I have a Ford Escort 1.4 Petrol Engine which has done 117,000 miles. I bought this vehicle last year and is running very well since then. I love this car and want to keep it running as long as I can. Many people suggested me to sell off the car because of an old machine but I think it runs better than other cars of this age. I had new head gasket in the vehicle and is well serviced since then. There is no blue or any other smoke coming out of the vehicle.

My car is currently giving 6-8mpl and is consuming about 700ml of engine oil every 800 - 1000 miles. It's initial pick up is fairly low(0-60mph in 22 secs) as compared to other vehicles. I want to know if this kind of performance is normal for this car or is below average and what should I do get it fixed?

Also apart from normal engine tune up which I have already done what all should I change and maintain regularly to keep it running? I am not sure about gear oil and any other stuff which might need changing at this age or any parts to be cleaned or keep an eye on?

Also my car when doing 70 - 80 mph on Motorways/Highways sometimes I feel front of my car sliding to either direction on its own even though I am holding the steering firmly. Even when I apply brakes on high sppeds my car tends to steer on its left even though I have got my tracking done & the report is OK. What could be the possible reason for that?

Please reply and help me out.
Many Thanks