I like FAL rifles and I have several but with all the many parts kits which came in and a variety of guys building them with varying degrees of competence I can understand how buying a used one (most all are used) can be a real crap shoot. Most are fixable as it is a design which responds to tinkering. On your failures...were they failure to feed, failure to extract, failure to eject? Check your gas piston as it could be bent. Remove the gas plug by bushing in the button or lever and rotating 90 degrees, remove the piston which is under spring pressure, remove the spring from the piston, remove the bolt and carrier, then insert the piston, sans the spring, into the gas block and it should drop through and protrude out the receiver end above the chamber. If it does not freely drop through then check to see if the piston is bent.
The holes in the gas tube towards the front are normal, actually there should be 2 in the 8 and 4 position on the tube. If the gas vent holes are in another position then your tube is not positioned properly and that could be closing off some gas from cycling the rifle. The half gas tube is normal on some rifles, especially the StG-58. Some half tubes are soldered in the gas block, some are screwed in and pinned.
It gets rather complicated so your best bet would be to read up on the design and try to fix yourself or take or send to a 'smith who is familiar with the design.
Be careful about shooting the rifle with the top cover removed as the cases could come straight back and ding your forehead real good. I don't recommend that. You should be able to tell if the bolt carrier is dragging on the top cover by manually cycling the action.
The FAL Files (
www.falfiles.com/forums) used to be real good at helping people with their rifles but now with over 14000 members you get guys responding who don't fully understand the issue and it can get confusing. It is still a great place to read up on the FAL and the problems you may encounter.
Good luck.