Countless lenses have been taken apart by me. And then put back together after everything was cleaned.

TIP: when cleaning elements use water that has a drop of dish liquid in it so that static electricity will not attract the dust. Then clean both sides simultaneously with an extremely clean soft tissue by turning the element between the two sides of the tissue.

What you REALLY have to beware of are the short lenses like 28mm or, worse, 24mm. These are VERY complex as to how the elements are put together and, just as important, which SIDE of the element is to be placed.

Many times I completely remove the dried up grease on the helical (with lighter fluid) and re-grease with a tiny amount of Vaseline. You do not need the large amount of grease that almost all manufacturers used when building the lens. Only Nikon was sensible enough to put only a tiny amount of this lubricant on the helical. The others put too much and, as a result, these old lenses become difficult to focus unless the dried up gunk is removed. - David Lyga