Your Crassula 'Moonglow' should be re-potted about every two years so that the potting mix keeps a good, gritty and fast-draining texture. If it hasn't been re-potted recently, spring is the time to do that. Move it to a pot with a drain hole and without an incorporated run-off dish (not good for succulents) that is up one size from the current pot. Mix 3 parts standard potting mix (with no added fertilizer) and one part coarse sand or Perlite as a soil mix. Fill the pot with the potting mixture until it is less than an inch from the rim of the pot and do not bury the plant any more deeply in the soil than it is now. Sprinkle the top of the soil with a thin coating of coarse sand or pebbles so the plant's lower leaves do not come into contact with the soil.

At the moment, the soil is old and will not be draining perfectly which can leave the top of the soil too damp, affecting the lower leaves. Check whether you also have a little too much space between the soil surface and the top of the pot. That creates a small, humid area under the plant and is often the cause of rotting lower leaves on the bottom of a succulent. Improving the soil, its depth in the pot, and creating a barrier to the soil surface will all help to keep the plant from deteriorating further.

While the roots are out of the old pot, check for dead or slimy, rotted roots and cut them away with a sterile scissor.  Going forward, make sure that you water the plant with tepid water, only in the morning and empty the run off dish within 15 minutes after watering. 

It is fine for the stems of the plant to topple over the edge of the pot and they often grow in a curving, gentle swoop. A heavier new pot may help with keeping the plant in balance. 

Courtesy of NYBG Plant Information Service