While I am not familiar specifically with guanidine hydrochloride, hydrochloride salts of compounds dissolved in water usually are corrosive to austenitic stainless steels like 316L, especially at this concentration. Aqueous acidic solutions containing chlorides can cause pitting, crevice corrosion, and stress corrosion cracking depending on the temperatures involved. I have personally observed pitting and crevice corrosion of 316L stainless steel in systems such as this at temperatures as low as 15 degrees C.