We just moved into a new house and acquired this playset/swing in the process. When we walked through before buying it I never realized how badly it was leaning. I am now trying to figure out the best way to straighten it and brace it so that it stays upright. The 1st picture is trying to show how bad it is leaning. The top of the playset is leaning far right as I look toward the level. The next I am marking in red, to the left and below where I am facing the level, where I think I should add support. Support will be added exactly opposite these two marks as well. Any other ideas?
A way to fix lean is to use a comealong until it is straight, and then screw a piece of plywood on the part that needs bracing. Paint the plywood to match, and you'd have a one or two walled "room" and a much stronger brace. Use lots of screws, not just ones in the corner, of course.
Your illustrated cross bracing on that side will not stop it from leaning the way it is leaning. That bracing would only stop it from leaning parallel to the slide.
If you want to stop the leaning perpendicular to that, you will need cross bracing in that direction also.
Diagonal pieces of ¼"x2" flat steel with lag bolts could stiffen it up but you will have to plumb it up before adding the bracing.
I used several of the ideas here including comealongs. I decided to go with some 4x4s to brace against the lean. I strapped these to the playset using two 20 inch heavy strap ties. Those are bolted into the set and bent into position over the top of each 4x4. I then drilled holes into the bottom of each 4x4 and added a 24in. re-bar into the ground. Finally, I included cross bracing (not pictured) and everything is solid after two months use. Thanks for the ideas!