GM engines to avoid/may need repairs more often -
Quad 4 - Head gasket eater/Head cracker, bottom end doesn't get as much oil as it should
3.4 DOHC - Head gasket eater, dist blockoff leaks badly, and requires head removal to fix.
3100/3400 - LIM gaskets LOVE to fail at random, keep a watch on them, as it will destroy the lifters VERY easily, also keep a CLOSE watch on the water pump, if it fails, you overheat, heads warp = you lose. 2.8 and 3.1 MPFIs experience the water pump problem also, but seem to be a tougher engine than the 3100/3400.
3.0 DOHC in Catera - Avoid at all costs. Very expensive to repair, and a all around nightmare to work on.
Early 80s V8 Diesels - Problems with intake manifold warpage, which leads to massive coolant leaks, and leads to bottom end damage. Also heads love to lift off the block and snap the head bolts.
Cavalier/Sunfire/S10/Malibu 2.2 OHV - Fairly good engine, but watch for the waterpump on these, if it overheats, the head WILL crack. Other than that, great engine on MPGs, but no torque monster, very slow and slow revving.
That'* all I have for now.