jbaj007 is right.
The "micro-encapsulated screws" are factory bolts that have on them, a Loctite type of chemical (usually blue) that prevents bolts from getting loose in high vibration and shock applications. Why this instead of say a lock-washer? Because there is a greater surface area of resistance with the chemical than a lock-washer.
The micro-encapsulation really just means that little tiny droplets of the "Loctite" type chemical is applied to the bolt. When the bolt is threaded into its respective nut or piece, the little droplets burst and chemically attach to the bolt's threads and to the respective attached piece. It is my understanding that this actually occurs at the microscopic grain level of the metals.
I have seen them used in window regulators and bolts mounting brake calipers. Non-wet applications: no oil, fuel or coolant.
The idea is once used, they should be replaced. I have found that using them again with a small dab of Locktite seems to rejuvenate the "micro-encapsulated" chemical.
My 2 cents
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)