Ans: The shield is attached to the outer race and it is a clearance between the outer and inner race. On the other hand the seal is attached to the outer with the inner race.
The main reasons of not using seals in all applications instead of shields, are:

1. Speed 2. Heat and 3. Starting Torque

The seal could cause problems in these areas due to its rubbing against the inner race and in the case of shield, there is a clearance between outer and inner race and then there is no such kind of problem.

Ans: No, everything is fine. The bearing must have a slight amount of movement. This is necessary for running clearance, so it does not bind. And say, before for doing this, remember to take a second to wipe off your fingers.

Ans: Bearings do fail for many reasons, but improper lubrication is there at the top of the list. And the rest are the following:

43% due to improper lubrication;
27% due to improper mounting;
21 % due to other causes and
9% due to reaching the fatigue limit of the metal.

Reasons for lubrication failure are following:
1) Incorrect selection of the grease base for a particular application.
2) Use of static or circulating oil in a improper manner.
3) Insufficient lubrication either in quantity or in required viscosity.
4) Deterioration of prolonged service without proper intervals.
5) Contamination of the lubricant and the bearing with foreign materials.

Ans: Yes, there is a right and wrong way to store bearings. You should store bearings in a clean and dry place.. Always use the oldest bearing first. Bearings are precision components and should be treated gently. Never drop them or handle them roughly. In fact, the less you handle them the better since finger prints can lead to rusting. It is necessary to measure temperature changes in your bearing storage area regularly because condition like condensed moisture forms could be harmful for bearings.

Ans: Over lubrication might be your problem. As unlikely as it may seem, over lubrication as well as insufficient lubrication of bearings used in high application, both are equally harmful. Over lubrication creates a drag on the bearing which in turn causes friction. Friction causes heat. The fact that your bearings are "well lubricated" is probably the source of your trouble!

Ans: Bearing lubricant should establish and maintain a micro film of oil between rotating and static members. The forming of the elastic hydrodynamic film is the result of a build-up wedging action of the lubricant between rolling elements and raceways.