I have a 93' Mazda B3000SE PU. It has 153,000 miles on it. It has a major oil leak. I add a qt. of oil every other day to it. The transmission is sliping out of overdrive after I drive it for about 20 minutes. It's an automatic. And just last week the muffler went out. My question is do I fix her up or do I trade her in on a newer model?? (Edmonds had a price of about $350.00 TMV & $1,200.00 to buy at retail). Thank you!!