how to install a new garage door opener

I'm new to this site and I need advice. We brought our home 5 yrs ago. The garage sit on a concrete slab with cement walk around the side and back. Every rain leaks under the walls. the wood is decaying. I know the best fix is a new gargage, but that isn't an option at this time. I've tried to run cauk around the edge on the outside(that what the sellers had done) but that hasn't lasted. Could I use roofers tar to seal the wood to the concrete? Any suggestion to buy time would help.

I contemplating replacing my garage door because it is not sealing appropriately at the bottom (water will enter the garage by the corners of the door). I have replaced the seal on the garage door itself, which did not help. I have a wood door and have been told that the wood is warped, thus causing the corners to be up and the center of the door to be flush with the cement. I have also been told that the wood door weighs more, thus the corners pull up and the center is flush with the ground, "a steel door will correct this problem" I have also been told that the cement is not level (which is what I believe is the problem) and there are two ways to fix the door, remove the bottom panels and get a custom made bottom or there is something on the market that is a seal placed on the cement. A plastic type material that forms around the door when it is down. However, the company did not know where someone could purchase this material. Does anyone know where to get this material? Or any advise would be greatly appreciated. The door is in good condition and I hate to buy something I don't need.