Please rephrase and elaborate in depth if possible, i didnt get it.
Ok so bg109 if you search the net you will see it is an additive you can add to your oil, you can put it before you do an oil change or half way throw a service cycle. It is designed to last one heat cycle then turn inert. but Personally i do it before the oil change. I don't see the point of putting something in to help clean out the oil system then not flushing all the crap out.
The bg109 removes and cleans the oil system and removes sludge and contaminates in your oil system, but the reason why I recommended it to you to use it for your application it also removes varnish, carbon build up and sludge from the piston rings allowing them to work as they were designed. Which would also help if your rings were starting or causing the low compression problem. Remember prevention is better than the cure. But don't think you can put in a can and you will have 200psi comp reading does not work like that.
In an engine carbon is and always has been the enemy. carbon is abrasive so in very basic terms, you are turning a lubricant ( your engine oil) in to a fine grinding paste which will cause wear which then over time kills your engine. This carbon turns to sludge over heat cycles causing all kinds of problems.
I always change oil every 6000 miles and use a bg service pack containing bg44k, bg109, bgMOA.
I hope this is In depth enough with out getting it to oil technology and metallurgy.
With ref to the intake valve, carboning of the valves it is a know problem with the r56 i have seen these valves so carboned up they have caused compression problems
This is why I mentioned about the inlet valves
Ps did you do you comp check with engine hot or cold
Hope this helps