does all cadillacs have headgasket problems?

No!!

The Northstar motor seems to have an increased likelihood of headgasket problems, particularly pre-2000. The other motors (4.x) tend to be less prone to this issue.

Yeah more common than most motors. Poorly designed studs lead to high headgasket failure rates. In 2004 the problem was pretty much eliminated, while post 2000 N* motors featured redesigned heads that sort of addressed this problem. If your looking to buy a Caddy look for a 2000 or newer.

If your looking to buy a Caddy look for a 2000 or newer.

Or 1995 and older with a 4.5 or 4.9 engine.

The main motor to deal with this is the aftermentioned Northstar, especially in the '97-'99 years. In 2000 they were redesigned to help allieviate the problem, but my '00 Seville did suffer a HG failure at only 54k miles. There is also an '01 STS at my shop right now getting it's HG's done. I only recommend the 2000+ models, though I would make 100% sure the coolant was changed and the maintenance was well kept up. The usual failing point is around 60k-100k miles, though some have gone earlier (mine), and some have gone out later (150k+).

I believe the old 4.1 (HT4100) suffered problems with HG as well, but that motor is long gone (thankfully).

I believe the old 4.1 (HT4100) suffered problems with HG as well, but that motor is long gone (thankfully).

The 4100 pretty much just fell apart. A lot of problems where due to it leaking coolant and the owners then running the car with low coolant and overheating the engine thus causing the HG issues. The 4100 engines in the '87 cars (last year for the engine) are just about as reliable as the 4500 or the 4.9.

Why bother with the HT4100? Aside from being unreliable, it'll get outran by a push mower!

GM pretty much cured the HG problem around 2000. Northstars from that point and newer now have oil pan gasket problems (between 50 and 100k miles). Supposedly about $1800, and no cure from GM other than buying a new gasket that will develop similar problem after another 50k miles.

Too bad for people who buy high mileage cars.