Is it just time that I get a new car?

I have a 1998 Chevy Monte Carlo with a 3.1 engine and has 211,000 miles. I love the car still and til now never any problems. I am having a few problems with it which hopefully I will be able to fix but I am not good at pin-poiting them. An ongoing problem is it slowly looses oil and engine coolant. The oil gets a bit dark but nothing out of the ordinary I don't believe, the coolant however gets dark I say, sludge I'm told. If this makes a differance or not I did use Dex-Cool at one point but no longer do. My car starts to overheat after 10-15 mins if I am not driving on the highway. About six mos ago after its routine check-up it starting running rough, seemed as though it wanted to die while sitting at a light, idleing hard, when going in reverse (still does this from time to time) it hesitates before moving then will "skip" but drives fine once out of reverse. About a month after that it acted as though she just didn't want to go anywhere, like I was driving with my parking brake on checked many times and wasn't but my brake light would stay on after starting it for a min or 2 and shut off. I checked the brake fluid-was fine, was due for new brake pads anyway so I did those and took apart the center counsel thinking I'd know what was wrong if I came across it (haha) of course nothing unusual to me besides all of it, could have done without the new pads but oh well, back together only 2 extra parts left with no clue where they go but no change and about 3-4 days later all good? No idea? Then a week or two later my security light would come and stay on everytime I'd start the car and 1 out of 3 or so times the air bag light also. What do you think? Do you recommend doing a flush and whatever else needs to be done? I hate to put the money into it if it will only be a temp. Fix but if it will last awhile I wouldn't hesitate a second. The car has been great for me and the body is in excellent condition. I would do some of the work myself but don't trust myself enough (although I think I'd eventually get it done)to do it all and I do not trust the mechanics and their estimates in my area (Twin Cities, MN) so if you know the reasonable price guide that would be great also! Thank you so much for your time and your patience with me! I try because I enjoy it but thats probably the start of all the problems right there. :Wink: