Your refrigerant is low. Pressure as measured on item 7 should be about 15.
Freon is a very "slippery" fluid and is difficult to contain. It's not uncommon for MBs to develop leaks after 9 or 10 years.
You will need to have shop check out your system. They will likely evacuate it and then recharge with proper amount of R134a along with a dye. After driving for a week or two, they will be able to inspect and determine where the leak is.
I know from experience that it is frustrating to have expensive A/C repairs when the car is little used and A/C seldom needed.
Some owners will try a temporary solution. Walmart sell R134a and recharging kits. It's easy to do and the A/C may work for a while. But not a long term solution.
Good Luck.