Brass monkey,
We do have the gaskets in stock but they only need to be replaced if they become damaged, they are not a consumable item.
Whilst taking the internals out of the shell will not affect your Rohloff hub guarantee, it really is a very bad idea.
There are several key steps when correctly reassembling the hub that you must get right. If you do not correctly reassemble the hub it will not fully function as expected. If this occurs the hub will need to be returned to Rohloff at your cost, they can easily see whether the shell has been opened and then rectify the problem.
We have several staff that have received Rohloff training in Germany to perform the procedure of disassembling and swapping hub internals correctly using specific Rohloff tools.
PLEASE NOTE
Rohloff state that "if you dismount the locking nut onto the axle (the aluminium nut)" your guarantee is lost.
Thorn Cycles Ltd do not recommend that you disassemble your own Rohloff hub!