The 1978 Buick Skylark on the GM A-body platform is mechanically straightforward but plagued by weak THM200 transmissions, carburetor issues, and typical late-'70s emissions complexity. The 231 V6 is underpowered but relatively durable; the 260 Olds V8 is a parts-availability nightmare; the 350 is the best bet if you find one.
THM200 Automatic Transmission Failure
Common · high severityTypical onset: 60,000-90,000 mi
Symptoms: Slipping between 1st and 2nd gear under load, Delayed engagement when shifting into Drive, Burnt transmission fluid smell, Whining or grinding noise during acceleration
Fix: The THM200 (M29) was GM's economy transmission and notoriously weak behind even the 231 V6. Expect complete rebuild or replacement. Rebuild takes 8-12 hours; many shops opt for a reman unit swap at 6-8 hours. Trans mounts typically shot by this point too—add 1 hour.
Estimated cost: $1,800-3,200
Rochester 2GC/2GE Carburetor Problems
Common · medium severitySymptoms: Hard starting when cold, especially below 40°F, Rough idle and stalling at stop lights, Black smoke from exhaust under acceleration, Fuel odor in engine bay from flooding
Fix: The emissions-strangled Rochester 2-barrel carbs have aged poorly—vacuum lines crack, choke pulloffs fail, and internal passages clog. Full rebuild kit with choke work takes 3-4 hours if you know these carbs; many techs just swap on a reman unit at 2 hours labor. Vacuum hose replacement essential during any carb work.
Estimated cost: $350-750
231 V6 Intake Manifold Gasket Leaks
Common · medium severityTypical onset: 80,000-120,000 mi
Symptoms: Coolant loss with no visible external leaks, White smoke from exhaust on cold start, Rough idle and occasional misfire, Coolant in oil (milky dipstick) in severe cases
Fix: The 231 even-fire V6 uses a composite intake gasket that fails where it seals the coolant crossover passages. Manifold removal requires carb off, all vacuum lines, and careful cleaning. Budget 5-6 hours labor. Do valve cover gaskets at same time—they're always seeping by this age. New coolant and oil changes mandatory after.
Estimated cost: $450-850
Body Mount and Frame Rust (Northern Cars)
Occasional · high severitySymptoms: Visible rust perforation on rear wheel arches and lower quarters, Sagging body or doors that won't close properly, Crumbling body mounts visible under rocker panels, Floor pan rust-through near seat mounts
Fix: A-body shells from the rust belt are often structurally compromised by now. Body mounts rot out completely; frame rails behind rear wheels rust through. Replacing all body mounts takes 8-10 hours with proper lift time. If frame repair is needed, you're looking at 20+ hours for patches and welding—often totals the car economically.
Estimated cost: $600-1,200 for mounts only; frame work $2,500+
260 Oldsmobile V8 Parts Availability Crisis
Rare · high severitySymptoms: Any engine failure requiring internal parts, Need for exhaust manifolds, water pump, or other engine-specific components
Fix: If you have the 260 Olds V8 (4.3L), finding pistons, rods, bearings, or even basic bolt-ons is extremely difficult—many parts were unique to this short-lived emissions engine. Engine rebuilds often require custom machining or NOS parts hunting. Most shops recommend 350 Olds or Chevy swaps instead, which is 20-30 hours for a clean swap including exhaust and mounts.
Estimated cost: $3,500-6,500 for swap
Steering Box and Linkage Wear
Common · medium severityTypical onset: 70,000-110,000 mi
Symptoms: Excessive play in steering wheel (more than 2 inches at rim), Wandering on highway requiring constant correction, Clunking from front end over bumps, Uneven tire wear on front tires
Fix: Manual steering boxes wear out the sector shaft, power boxes leak at the sector seal. Idler arm and center link ball sockets also wear. Full front-end rebuild (box, idler, center link, tie rods) takes 4-6 hours. Alignment essential after—add 1 hour. If just doing box, it's 2-3 hours on a lift.
Estimated cost: $550-1,200
Buy only if it's a rust-free southern 350 V8 car with documented transmission work—the 231 V6 is tolerable, but avoid the 260 Olds and any northern car with frame rot.
AI-assisted summary drawn from NHTSA recall data, our labor-times database, and platform knowledge. Not a substitute for a pre-purchase inspection on a specific vehicle.