Shunyata has a new fuse that they ssy sounds better than the one used originally on the early units and I would go with that........Oh, Mothra Research makes a slug, but it is a bit larger than will probably fit the unit, but see the following:
http://www.mothraresearch.com/slugs.html
The entire Mothra site is full of things of interest, especially the section "Recreating Life" :-)