40-odd years ago, I found out that the slab of my house in Las Vegas was poured over a gully that filled with running water every time it rained, and had washed out much of the support for my house. Found this when a 30' hypotenuse triangle of the front left corner cracked and slumped just before I had to sell the house and leave the country. Back then, the quote to pump concrete under the slab to support and raise it was $10K. This is 1983. The house was only worth about $50K at the time. Before the cracked slab. There should be someone in your areas that could fill the space under your slab and save it. But removing it and replacing it might be cheaper. And how I wish I had a garage and slab with a lift on it!

Keep the lift that works. I miss my lift, but can't use one in my tinny detached 12x18x7' (WxLxH) garage. Replace the concrete, make it a UTube vid, write it off, and giggle at the knowledge you just made a difficult job look spectacularly easy in a 15 minute UTube video.

Get a core drill and cut some inspection holes to get an idea of how extensive a problem it really is. There is a chance the problem is not as extensive as it seems. Maybe you can cut out the mounting areas and pour deep pilings to mount the lift and solve any other issues as they are identified. Just my 2 cents.

What I would do: Pump concrete or foundation epoxy underneath. Bandaid? Sure. Better than what you're standing on? Absolutely. Relatively cheap, safe, non-intrusive and can be done in a day with minimal disruption.

I would jackhammer out the concrete under the lift (maybe 10' x 10'). Get a Harbor freight jackhammer and resell it after your done. Pour a new 6-8" steel reinforced slab in the hole. Reinstall lift. Seal water ingress. If you're really paranoid, drill some holes in the rest of the floor to check for voids.

If you could find a cheap piece of 1 and 1/2" inch steel plate as long as the lift is wide and wide as the hoist mounting surfaces, you could anchor that to the floor and attach the lift to the plate, but I doubt that you could find a piece of 1 and 1/2" steel for cheap enough (including transport to your shop) to make it cost effective. It would totally solve your hoist problem if you could though.

You’d be surprised how cheap you can get a solid second hand lift from shops that are going out of business or changing locations etc. I had a mechanic that bought a very solid lift for $600 about 15 years back (do whatever inflation calculations you wish)

I would have someone come in and foam level it. If you really feel unsafe with the lift then get a set of quick jacks. The load will be spread out over more area.

Wes just did something like this by pumping concrete below bhis slab. I'm still jealous

Looks like that lift was already modified with 2x2 bars to spread out the weight forward and aft so guessing the installer new it was sketchy at best. What would I do today , not look for info in the comments but get someone who knows what they are doing to look at it. What would 25 year old me do ....... get some 8 ft long 3/8 thick 2x6 angle or square stock and weld the bajezuz out of it wont fall forward or back and make sure the tops of the hoist are held apart with some 2x6 1/8 wall as a spreader. The 5000 ish LB lifting pile of obsolete you can use until you save up to do it right then. Final thought, get it fixed or out before them kids are old enough to be around when its in use or wanting to use it themselves. Peace

I would see if you could pump something underneath it to at least stop the water ingress. Then if i had room id look at adding on to the shop, putting a new thick slab in.

You’re going to have to get in there to see how bad the damage is. And I mean, is it just that area or has it spread to other parts of the garage. That what would scare me.

Could you just pour a new slab on top of the old one?

hopefully only the garage and not your house. I'd make a new slap, and use the old lift for as long as it works

I’m curious any updates on this?

any update dude?