Replacing front CV axles?

They get old, dry rot, and rip. As far as replacement, most shops just replace the half shaft which includes the axle and both CV joints. This video shows the job being done on a similar car but the process is the same.

https://youtu.be/XeqT-_fwVQg

That is what I would recommend. A half shaft is around 150.00 each and labor is around 3 hours for both.

Do you mean the seal IN the axle housing or one of the CV boots?

If you mean the one in the housing that seals the stub shaft, Remove the drivers side half shaft. Then you can remove and replace the seal. Check the bearing while you have the seal out. It can also be replaced while you're there. Just be careful installing the new one.

Once you have the new seal in it would be a good idea to check/change the front axle lube in case any was lost through the bad seal.

OK, to pull the half shaft is simple. First you need to jack up the front, pull the tire/wheel off. Now you need to remove the nut in the middle of the hub. Next step is to use a block of wood to break the axle loose from the hub, one good whack on the wood block on the end of the shaft should get it loose. Next you want to position a jack under the lower A arm. You will also want to remove the brake caliper for extra room. Just remove the two caliper pins and hang it out of the way. Now remove the pinch bolt from the lower steering knuckle area. Then GENTLY pry the ball joint free from the knuckle. Now you can pull out on the knuckle and push in on the axle at the same time. Now that you have the axle free on the outer end. Reach in around the inner tri-pot joint with a couple pry bars. You just pop the axle free (there is a small snap ring inside) and it will come out. Change the parts and reverse the procedure to put the axle back in. Torque the pinch bolt to 30 ft. Lbs (good and tight if you don't have a torque wrench) The large axle nut gets torqued to 120 ft. Lbs.

It sounds like it is your CV Axle, However, it could also be the wheel bearings. To check these, jack up the front of the vehicle stabilize with jack stands. Then crawl under and grab the cv axle at near one of the boots, now twist it, does it have a lot of play? If not do same at the other boot on same axle. If has a lot of play replace cv axle. If all feels good and tight then check bearings. To do this just grab the wheel at top and bottom, now pull out at bottom and push in at top, it should have very little to no play. If has a lot of play then replace bearing. Check both driver and passenger sides.

Depending how the other cv joint is you should only need to replace one. It is recommended to replace both. Check with a local auto store, most have axles that are rebuilt and can be put on in one piece.

That looks like broken pieces of the CV joint cage that holds the steel balls.
Why do you not just go take the complete axle along with the CV joint from a car in a salvage yard?
You can find if there are any 1987 Chevrolet s10 Blazers near you with this nationwide database of salvage yards.
http://www.car-part.com/

You can just purchase the entire CV axle assembly from Summit Racing for about $50.00.
https://www.summitracing.com/search/year/1987/make/chevrolet/model/s10-blazer/part-type/axle-shafts-direct-fit?N=4294950300%2B4294951398%2B4294949276%2B4294945517&SortBy=Default&SortOrder=Ascending&keyword=cv

Summit Racing is usually pretty fast, like two to three days.
It's hard to say what may go wrong next, but anytime you notice the boot torn you must replace the boot and grease so the CV joint doesn't wear out from no grease.