I'm going to try and keep this brief, but I understand why people get away with charging $200-300 and a 6-9 month wait list for vintage scope repairs (crosshairs.)
The Unertl I got from the Auction needed its crosshairs replaced, this is how i did it. Paid Amazon $9 for a cheap little mini bench vise, paid $10 to some ebay guy selling packs of 0.001, 0.0005 and 0.0015 tungsten wire, and a bottle of gel super glue from ace hardware for $6. Scavenging some lead fishing weights from my dad's garage, and a oil paint pen.
Step 1. Clean off the surface of the 'cell', a small brass(?) tube that the crosshair sits on. I used 400 grit sandpaper on a granite countertop. Flattest surface I had.
2. Place cell in mini-bench-vise using the plastic riser accessories. I left the leveling screws in the cell to keep them from otherwise getting lost, they are small.
3. Use a exacto knife, or micro wire drill to drill out the holes filled with epoxy from original crosshair installation (I think this only applies to some vintage scopes, as others use small screws, and some have other attachment methods like soldering (Lyman?).
4. Use an exacto knife to cut as square-as-I-could-manage, very slight channels across the surface of the cell, for the crosshair wire to sit in. (don't use a needle file, that was one of my major mistakes. ABSOLUTELY DO NOT USE A NEEDLE FILE.) You can try without cutting into the cell, but it will make lining up and holding the crosshairs much more difficult. You don't need to cut deep, just enough to make the barest hit of a v-grove to help center and hold the crosshair wire.
5. Carefully put a fishing weight on the loose end of a wire, then cut it off, and place a fishing weight on the other end. For thicker wire you may need to add more weight to make sure it is straight when sitting on the cell. A very small pliers helps with this. Depending on how you get your wire (there was on ebay seller that just wrapped it up in a loose set of loops with a bit of tape, and the other, much better seller, who attached the 3 pieces in a straight line to a stiff white paper backerboard.)
6. Glue in one side ONLY at a time, and let cure. This gives you some adhesion to work with to make sure when you glue the other side of the wire, that you can pull it just a bit to make sure its straight. Very thin wire (.0005) is absolutely a pain to work with tho. It kinks, breaks, bends, etc., very easily. I eventually just gave up on both 0.0005 and 0.001 and used the 0.0015 for this cell. I went through 3 attempts with 0.0005 and two with 0.001. The wire can still easily pull out of the glue, so be careful. I used a toothpick to very gently press down on or move the weights to make tiny adjustments.
7. Repeat for cross direction.
8. Use a black oil paint pen, or nail liquid, or similar in a dull finish to cover the exposed brass otherwise it will be highly visible when you look in the scope.
9. Let cure, and re-assemble.
This is my second best 'attempt', I was planning to use it, but broke it when trying to assemble.
If you can't quite see it, but the right side is slightly bent, and the vertical alignment was also off a bit.https://i.imgur.com/esNxtXJ.jpg
The last attempt, pre-blacking, looks much worse through cellphone + magnifier.https://i.imgur.com/R0EnmWr.jpg
But is I think almost perfectly straight, if you didn't cover the exposed part of the cell with paint/etc, there'd be a giant bright brass ring staring back at you with a lot of glare.https://i.imgur.com/GggBTJe.jpg
Installed with eyepiece on, and dialed in.https://i.imgur.com/how0Vk2.jpg