2 locking nuts on our Tetratec ex1200 have sheared. We have used cable ties, which work, but would prefer new lock nuts as it makes cleaning easier. Tetratec do not supply lock nuts as spare parts. Has anyone else had this problem and are Eheim lock nuts likely to be compatible provided we get the right diameter? The filter is 2 years old and we have had a replacement head under warranty already. The spares list is very limited compared to other makes (something we didn't consider when making the original purchase). Any help or suggestions welcome. Tank is 150L and filter does its job in spite of fragile parts.