For a 30+ year old machine, the problems are just that; being 30+ years old.
I've had many bikes over the years, but I've walked away from many possible deals not because of the bike, but because of the covertness of Billy-Bob and his Emporium. Alot of 1000's have led rough lives but if the PO is honest, and the bike is what you want....
For starters, if it looks like it has been stored outside---rust, faded paint, etc., walk away from it. You will have nothing but problems.
Assuming it passes that test, look for:
-cylinder compression. If you can't test compression, see if you can at least pull the spark plugs. They will tell a story.
-look for rust perforation on the frame under the engine, especially the centre stand pivot.
-mufflers will usually rust out underneath, where the exhaust pipe joins the muffler.
-put bike on center stand and check for run-out on both wheels. Make sure they are straight.
-open the side cover on the left side of the fake gas tank. See if the wiring has been butchered or if it looks intact.
-Open oil filler cap and look for white milky stuff inside. It means the antifreeze is leaking into the oil.
-look under the bike, on the garage floor after it has been parked overnight. Even a few drips of oil or antifreeze on the floor means it could be leaking through the weep hole which means the water pump seal is shot--a big job to fix.
-inspect frame carefully for cracks, dents or welds.
-watch the voltmeter while the engine is running. It may drop a bit below 12 volts at idle but should easily climb to 14 if you rev the engine a bit. If not, then probably alternator or regulator problems
-turn the kill switch off and crank the engine for about 10 seconds. Make sure it will still crank strongly. Otherwise, battery is likely weak.
-look for corrosion in battery compartment.
-check that speedo and tachometer both work and that the needles don't bounce around. Look for water droplets or misting on the underside of the glass.
-see if the rear shocks are the factory originals. If so, they are shot and you will need to replace them. About $200
-If possible, inspect the inside of gas tank for rust.
-check that neutral light works. If not, it is a PITA to fix.
-watch the exhaust while engine is running. Blue smoke means bad piston rings or valves, black smoke means carb problems, white smoke with a sweet smell meansblown head gasket or worse.
Unfortunately,you won't know what condition the drive shaft splines are in until you open it up. I have never heard of problems with the rivets on the Comstars. Mine is 30 years old and still tight as when new.
Thanks for the information gofast.
I have an"opportunity" to by a '75 gl1000 for a grand. However the paint is faded and there are some other cosmetic problems. It also ride hot???? I know its going to take some work to clean it up. But I am wondering whether its worth it or not.
I will go through the test you mentioned and try and gleam more form whats there. I just wonder if $1000 for a running '75 Goldwing is too much?
Hard to put a price on it because of regional differences in pricing, supply/demand etc. My gut feeling is that for $1K I would want it to be in better than just running condition i.e. always stored indoors, well maintained, etc.