Welcome to the the club.
It is infamous Lance design, where you have horizontal steel chanel under the slide and then you have vertical steel behind the jacks, but they are about 2" short to meet, so the critical stress point has some stapled toothpicks to handle the load.
I pulled slide out and put bigger steel chanel inside, overlap it with corner steel and bolted together. Had to pull some siding in bathroom area to get new steel under the sink, where Lance has structural junction.
Than I add additional aluminium angle outside the frame for extra support, screw everything together every few inches and reglue the siding.
Lot of pictures how the frame is build on Lance forum, where Captain made great pictorial from fellow member camper rebuild.
