Yes it could be the valve guides that are worn. This can cause the problem you are having. Usually the problem is a blown head gasket and this happens quite often. Since you have already replaced the head gasket I am going to assume that this is not the problem. You could have a warped head, but we will leave that for later.
Another problem is that many people tend to use the WRONG OIL. This engine should use SAE30W oil. DO NOT USE 10W-30 oil. The multi-grade oils will cause excessive oil burning and will wear out the rings and pistons much quicker. Only use a multi-grade oil on these engines when the temperature is below 30 degrees F.
There are only so many things that can cause this problem. Other than what we have discusses, some other possibilities are:
1. the oil dipstick seal may not be sealing correctly. This will cause the crankcase pressure to be off and it will push oil out through the valve breather and into the carburetor where it will be burnt.
2. Check the oil dipstick tube at the bottom also, there is usually a sea at the bottom as well as at the top. Same issues can occur.
3. If the engine is overspeeding, it will burn oil as well as give you a good chance of blowing the engine. Check the RPM's to make sure that they are not running more than 3400 to 3500 max.
4. There can be a pinhole in the block caused by poor castings. This will cause air to enter into the block and cause oil burning. These early Courage engines were not built very well and were built in China where they have much lower build standards.
5. Double check the head gasket and head.
6. Valve guides can be worn and cause oil to burn because it can be pushed through the guides.
7. The piston ring could be worn or broken causing this problem. Also an out of round cylinder can cause oil burning.
8. A burnt piston can cause this problem as well.
9. Any Gasket on the engine can be leaking .... allowing air to pass into the crankcase, causing a crankcase imbalance and push oil through the oil breather .
I hope that this can give you a few more things to check and I hope you find the REAL problem.
Since I am only having the pulg oil fouling in the left cylinder, wouldn't you rule out item 1, 2, 3,4 and 9 of your list above?
On # XXXXX above since I have 150 PSI in both cylinders wouldn't I rule that out? broken rings should cause cylinder scoring shouldn't it and there is no scoring in the left cylinder?
So would that leave me with the only possibility being either # XXXXX or 6 above?
That is possible. (5 & 6)
A broken ring usually causes a lack of compression as you said, but depending on how it is broken and which ring it is, it may not affect the compression. If it is the oil control ring that is broken or worn, the two top rings, which are the compression rings, are the ones that control the compression.
There is no real rhyme or reason as to which cylinder will burn the oil when the seals on the dipstick are bad. It can be one or both of the cylinders that will be affected.
As you also suggest, My first guess is that the head gasket or the valve guides are most likely the problem'
One of the biggest problems that we have had on these engines is that the VALVE GUIDES tend to MOVE out of position and stick up farther than they are supposed to. Tis is caused by overheating.....and sometimes just because they were not installed correctly. Look at the guides after taking off the valve cover and see if they are sticking up too far. Usually if there is a problem, one f the guides will stick up farther than the other. You should also check them against the other head.
Hopefully this will help.