I have really enjoyed using the Exstik 100. I have had this unit probably for 2 years, and I think the electrode is not consistent anymore. I have done the triple cleaning as by Pav, and still the unit is so variable that I do not trust it. I would like to replace just the electrode. Anyone with recommendations on this? It looks like my choices might be the 105, or the 115 refillable electrode. I am wondering about the refillable element of this - not sure how that works out. I realize the electrode is about 50% of the cost of a new unit...