Have any ideas as to what my problem can be?

Im using a high mileage synthetic oil.

 

check foe symptoms of a blown headgasket

 

check your coolant, if its milky its the HG, if not then you have a bigger problem....could be blown oil rings, Bad valve seals, or a clogged PVC pipe

 

could also be a rear main seal leaking. running synthetic after using convention oil tends to leak past seals such as the rear main seal. 8 dollar gasket but a pain in the *** to replace.( removing the transmission and flywheel and clutch if its a 5 spd.) usually when the rear main seal goes it will drip on the exhaust and you will smell it. if its a 5spd it could have glazed the clutch and flywheel and need replaced as well or scuff and clean it really well)

 

The coolant is fine.

Any idea as to how long I can go driving it around and adding oil every week?

Im not experiencing a loss of power at all. And by the way it is a 5 speed.

 

Do you see wet oil on the engine? if so where?

Check the oil pan and rear seal as well.

I have head gasket oil leak and been adding oil for a few years.

 

as long as you keep adding oil it could very well run fine for quite some time. I wouldn't consider adding 4 quarts of oil every month very practical though.

 

Do a coolant system pressure test or a cylinder leak down test.

 

Depends if you get oil for 2 and change a quart, still cheaper than engine work.