Sorry bud, not rebuildable. Best to replace with new aftermarket replacement shocks.
This is what I did to mine to buy some time till I get new shocks.
I drilled a 1/8" inch hole close to the bottom of the shock no closer than 1/4 inch from the weld.
Flush out the old oil with carb cleaner or your choice of solvent. I CAREFULLY used gas.
Be sure to let it air dry overnight.
Use a syringe and fill the shock with oil.
You may find it works best to extend the shocked as you are injecting oil as it creates a vacuum inside.
Do not overfill the shock. With the shock fully compressed... that is all you're going to get in there.
Compress the shock completely a few times and be careful while you are doing this but you want the surplus oil to come out of the hole...placed at the top of course.
Catch this oil for use in the other shock.
Expand the shock fully.
Clean the area and MIG or TIG weld that small hole shut.
Do not clean with brake cleaner as the residue can be lethal when you weld.
I found that if I had someone slowly extend the shock as I began to weld the oil didn't try to contaminate my weld. YMMV
When you compress the shock it should move to full compression travel and back out without hydrolocking.
Something that I found out by reading forums is the shocks are one way shocks. Even brand new they sucked as it has no dampening and only rebound. So that's all you're going to get but it's still a lot better than the pogo stick that you had.
I am doing my second shock tonight. I learned a lot from the first one and that's why I say to make sure your 1/4 inch above that weld at the bottom of the shock. If not you will find the bottom of the shock is solid and you may be drilling through solid metal or, like me, half through the block and half into the working resivour of the shock...and BREAK THE BIT.
Start saving your money:
http://www.japbikespares.com/honda-mt25 ... orbers-blk
http://www.progressivesuspension.com/pr ... es-dampers
Rick