volvo 240 dl wagon 1990 oily discharge from tailpipe

[binky1]

Just purchased 240 dl wagon w/ 191000 mi. Check engine light is on.
Had to have heat cover for exhaust welded & Meineke service mgr said car is running rich. What does this mean in terms of repairs needed?
Also, I noticed oily substance spraying out from tailpipe when it sits warming up in morning. Gas mileage is poor. Seller said I should get 20 mi/gal. This is my first volvo. Have I bought into a money pit? I am no mechanic.