Succulent is turning transparent and slimy - what should I do?

That sounds less like a characteristic of the plant itself and more like rot that's already pretty far gone - transparent and slimy usually means the tissue is breaking down. At this point, the only thing that helps is to cut away the affected parts generously (ideally with a clean knife) and repot the rest of the plant in dry substrate, preferably cactus soil or perlite mixed in. You shouldn't water it again until the soil is completely dry - succulents prefer it too dry rather than too wet. If the whole plant is already mushy, you can still try to separate a few healthy leaves and place them in dry substrate to develop roots, but honestly, that's usually the end of it.

When a succulent gets slimy, water is the main culprit - too much of it or the wrong conditions lead to root rot, and then the plant looks exactly like you're describing. It happened to me with an Echeveria that I watered way too often. I noticed the lower leaves started becoming translucent, and when I took it out of the pot, the roots were dark brown and mushy instead of light and firm.

Here's what you need to do now: get the pot out of any standing water (if it's still sitting in it), replace all the soil with dry, loose substrate - cactus or succulent soil mixed with a bit of sand or perlite is ideal. If the rot's already crept too far up into the stem, cut off the healthy parts (a single leaf often does the trick) and let them dry in the air for a couple of days, then stick them in dry soil - they'll grow back. Throw away the old plant if it's completely gone.

After that: water way less. Succulents do need water, but only when the soil is really dry - so maybe every two weeks in fall and winter, similar in summer depending on how warm it is. Standing water is the enemy. And make sure you have good drainage - the pot has to have a hole, otherwise water pools up and your new plant will have the same problem.