Yes, please excuse me you did post the config already so I should have realised you are the server owner.
In your config you have 919 and 29 twice. You should take out the second lines 919 and 29, it may be breaking things. In GC version 2.0.12.1026, each ID needs the metadata, like this:
Also it's best not to have the blank lines in between: just have one ID on each line.
---
If that doesn't fix it then I'm not sure of the exact reason for this problem; even though I'm the guy who coded the sealer, and I'm confident it was working correctly by the time I'd finished it, that was around 9 months ago now and I don't remember what exactly changed from version to version. Could be version 1026 is not working correctly. Looking at the changelog, there were
some sealer changes after version 1026.
Unfortunately, modpacks like Tekkit "lock" you to an out-of-date version of Galacticraft unless you are willing to update manually.
(I don't know why that specific GC version was chosen, and I have suggested to the Tekkit modpack makers they should update but I don't think they have any interest in making more 1.6.4 updates of Tekkit!)
If all the players on the server are your friends, I recommend the server and all players update to Galacticraft 2.0.14.1096 (just download its files and replace the Galacticraft files in your Tekkit folder). That version of GC will work fine with all the other mods in Tekkit, probably better than v.1026. The Technic Launcher might sometimes ask you if you want to "update" your Tekkit because it detects you do not have the "official" version 1026 of Galacticraft, so just answer No when it asks.
If using GC 2.0.14.1096 is not an option for all players (i.e. some players are locked to version 2.0.12.1026 on the client) then you must not update the server beyond 2.0.12.xxxx because a Galacticraft 2.0.12 client cannot connect to a Galacticraft 2.0.14 server. But you can still update
server-side only from 2.0.12.1026 to the last 2.0.12 version which is 2.0.12.1059. Get it here:
http://ci.micdoodle8.com/job/Galacticraft/1059/ I'd definitely recommend that for the server, it's better than 1026. There is no problem if a Galacticraft 2.0.12.1026 client connects to a Galacticraft 2.0.12.1059 server, everything will work. Changelog:
http://ci.micdoodle8.com/job/Galacticraft/changes
HTH
Any more problems, please:
1) Make the simplest possible build to test the Sealer, like a Sealer in a 2 x 2 x 2 room of stone with 1 wall made of Hardened Glass
2) Test in single player as well
3) Post your server log from server startup to the first time a player goes to a base with a Sealer, I am looking for any error messages in the log from the Sealer ID code