You say it "goes through several sets of leaves in the Spring/Summer". A Lithops should normally produce only one new set of leaves each year, grown during winter to emerge in spring. Extra sets of leaves indicate overwatering, possibly too little sun, and such plants are unlikely to flower.

Old plants can develop long stems wrapped in lots of dead leaves, not very attractive. Going through several pairs of leaves each year would make this happen all the faster. I try to tidy up the old leaves each year. By about this time in summer they are so thoroughly crisped by the sun that they pull away easily. If you leave them for several years, layers of them can become baked like armour and are much harder to clean up. It isn't strictly necessary to remove them, in the wild they can remain and provide extra protection, but in cultivation they are a place for pests to hide and mould to start.

You can repot now, or leave it a little while if you are in a summer heatwave. Leave the plant completely dry for a couple of weeks after repotting. Use a soil with very fast drainage, possibly a clay pot, as it sounds like you need a little help to stop the plant getting too much water. Don't expect miracles this year, any flower bud may already have aborted or turned into an extra pair of leaves. The fresh soil should give an old plant a real kickstart for next year. If you can avoid all the energy going into many new pairs of leaves, it should divide again fairly soon. Some species though, are very reluctant to divide beyond two or four heads.

In future, try to water until at least the end of September, this is the normal time you should be seeing flowers. You probably know when to start watering in spring, don't do it by the timetable but wait until the old leaf pair has dried up. Only think about watering in summer when the plants is showing wrinkles that don't go away overnight, then wait another few days! You can water more freely in autumn but make sure you stop as soon as the plant flowers.

the fact that they have only flowered when you first got them means that they are not growing well, whether it is lack of sun , poor soil structure, overwatering, etc.

it sounds like your plants are surviving, not thriving. do everything that shrubs-n-bulbs said, and make sure they are really getting enough unobstructed sunshine and good air circulation.

good luck!

Just as a way to show what I was talking about (and I'll follow what you said):

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Wow! There's a lot of old leaves stacked up there. Will they easily pull away?

I'm still a neophyte myself. But Shrubs and Xerophytes advice seem very sound. Should a larger sized pot be used?

They seem a little cramped to me , but I'm notorious for using oversized pots...

Yes, it could stand to be in a larger pot but make sure the soil drains well so they are not sitting in wet soil for too long. Shouldn't be a problem in a clay pot.

They are over-watered and under-sunned, tidy them up as best you can and put them on a diet ;)

can i get maple syrup with that stack!

Also maybe think about trying a fertilizer. I use a brand Cactus Juice for all my cacti and succulents and its done me pretty well so far. Its a liquid fertilizer, so you mix 1tbs/gal water and you place your pot into it and let it completely saturate the soil, with some plants this can take longer than others, it all depends on how rootbound the plant is. I normally let mine sit for a few minutes then let it completely drain out completely. I recommend you do this process when you normally water too as it hydrates the plant better. But fertilize every other watering during times of active growth. You want it to be in well draining soil, so if you do repot your plant I recommend Black Gold Cactus mix, ive had success with it, only complaint is that it has alot of perlite.

If you get the plant on a good water schedule, give it some good soil, and give it a little fertilizer, along with giving it adequate light, bright but not direct light, i recommend a south(east) facing window, there's no reason this plant shouldn't bounce back and with proper fertilization you should see flowering in a couple of years.

mj

Not sure if you noticed date of this post, it was 2007...probably late to give advice to original poster.

New tips are always welcomed and may help someone else, just wanted you to know how old & inactive this thread was.

BTW, I do not know much about lithops but I wonder about the 'watering & fertilizing' schedule you are suggesting for this plant. Lithops have somehow different watering needs, and many ppl kill them if watering often.

I also wonder why you think perlite is bad for succulent potting mix - most of us use a lot of it, or pumice if readily available, for fast draining potting mix.

Lots of ppl here use mix of cactus&succulent soil + perlite, and mix it 50/50. I make mix of only chicken grit and perlite and some turface - no soil at all.