Cracked tanks may not leak and can stay that way for years. However, there is no way to know if the crack is going to expand or start leaking. If the tank or toilet is not replaced, then you may want to caulk the crack for a little added protection.
Cracked tank lid
Cracked tank lids often can be repaired. If the lid is past being able to repair, then they may be replaced. Older toilets may not have lids that are still obtainable from the manufacturer.
Loose or wobbly
Over time toilets may become loose or wobbly. The first thing to check is if the bolts holding the toilet to the floor are tight and if they have a washer and nut on them.
If the floor is not level, the toilet may wobble back and forth or side to side. Generally a triangle shaped shim will correct this. Merely get the right thickness of a shim, trim it to fit and slide it between the base of the toilet and the floor.
Loose or cracked toilet seats
Tightening or replacing easily solves this problem.
Who to consult? Plumbers and qualified handymen.
Home owners can do much of the maintenance and repair type things in their bath rooms. Plumbers and qualified handymen are usually the ones that do the most of this type of work.