Given that you had a good starting experience with scraping on the Z-axis I guess youīre hooked now.
Since your gib only rides on a burr you have to find a way to cut the burr in the dovetails sharp corner. You could break a sawblade into pieces and line them up parallel so you can saw down in the dovetails corner. Itīs a pita but it works. Or you can get a knife file to reach in down there. First of all, inspect with a torchlight. Take a piece of toilet paper and run it in the dovetail. Youīll see and feel where it grabs due to the burr.
Since you already pulled the gibs and the slides, measure the ways with two precision pins and a micrometer to see if they are parallel. If not correct. On some of these machines, youīll find that not only the gibs are not parallel, they are not even in the same plane. In this case, blue up the seating surface of the base and see if it is straight or what is the deal with it. Mine was hollow in the middle, this leads to a crooked way when you bolt it down for milling it parallel. You bent the base, cut the new dovetails parallel, open the fixtures and presto, it bends back into a banana.
So first mill or file/scrape the base lower side flat, turn around, then remill the dovetails on top. You can maybe shim the base, too so it sits flat before cutting it.
Donīt forget to mill a side of the base straight in the same setup as you mill the dovetail. You may have to index in the casting with a DI later on and then a reference surface comes very handy. While you have the casting on the mill also make sure to mill the seating surfaces for the leadscrews rectangular to the dovetails. They are off more often than they are straight. No problem with a normal ACME screw but in case you think CNC sooner or later the screws may bind if the seating surfaces are not perpendicular. Itīs easy now to do it, it will not even cost you 10 minutes.
Bad thing about scraping in a Sieg machine or one of itīs clones is that they used 55° dovetail angle. I measured mine, decided that I want to go down the "fix me" road but not with 55° but with standard 60°. In effect, I remilled the ways to 60 degrees, cut the whole shebang in one setup so everything is straight and parallel and then, from a known straight surface that is parallel to within 0,001" I started scraping. This works pretty fast. The 60° remove about 1/16" from the dovetails width. To compensate, I made gibs that are 1/16th thicker, a huge increase in stiffness, too.
This will remarkeably stiffen up the machine. You can bend the original gibs easily by applying too much force and you have to do it only once. Even using the lock down screws can do this. Not a problem with my thicker gibs anymore.
Another thing: Youīll be surprised what youīll find under the bondo. Keep a little bit of cast iron rod nearby. You can cut a thread on it and glue in plugs with loctite 248 in locations where our chinese friends drilled holes that were not right and filled them with Bondo.