Well I seem to be having this odd issue with air bubbles building up in side my loop. Recently I notice temps go up and i checked the loop and I had lots off air in the tube, so I took the system apart and thougt that the pump wasnt working but then after testing it it turned out it did. As I tried to blow out the liquid from the loop I noticed that it was very hard at first as if something was blocking the flow. I finally got it to flow and re-did a few iffy connections and changed some tubing. I got the system up and running but it did seem to be running a bit weeker than usual. I spent a lot of time getting any extra air out of the system. Now every day I watch the loop and there is an air bubble that seems to be growing very slowly.

Any ideas what can be causing this?

Do pumps get weaker as they near their live span or do they just give out?
Is it some kind of buildup in the system clogging it?
Can the radiator have a hole? althou there is no visible leakage anywhere.