Memo from last year telling us not to back up precip

yes...FAA memo clarified that we would NOT back up the P...3...6...or 7...pcpn amounts if they were missing on the metar. I believe you are correct in giving the NWS rainfall amounts obtained from the manual gauge.

ASOS backup requirements are defined in FAA Order JO 7900.5E Chapter 6. There is nothing in that document that directs CWOs to backup precipitation amounts. FAA Order JO 7900.5E Chapter 9 paragraph 9.20 is titled "Precipitation Amounts (Automated)". They are not provided via manual means. The applicable paragraphs in FAA Order JO 7900.5E Chapter 13 regulating encoding of precipitation amount remarks also note that they are "Automated Only". This is why FAA added clarified with the memo because they had noted some CWOs manually editing the ASOS precipitation amount remarks even though the Order directs them not to do so.

The FAA has jurisdiction over the aviation surface weather observation program, not the NWS. The NWS cannot tell you to do something that is not required under FAA policies and regulations. The only CWO sites that need a manual rain gauge are those sites listed as snow depth reporting sites in FAA Order JO 7900.5E Appendix F, because one would be needed to perform the measurement for augmenting Water Equivalent of Snow on Ground remarks.