Well. after much chagrin, the way you get into the Nimbus wooden boxes is by releasing the 4 screws that are in the rubber feet. Then the unit just slides right out of the box. I identified the following:
mometary SPDT switch with white plunger as C&K part # 8125SHZBE Switch, P/B, Sealed, SPDT, ON-MOM, Plunger, .250" Flat Bushing, 0.4A, 20VAC/VDC, Solder at $4.04 at Alliedelec.com, and
there was 2 types of buttons used by Sensor Instruments: a small very boxy round button and a fatter concaved button, I am not sure which came first, but my temperature monitor and precipitation monitor have the smaller buttons and the wind sensor and barometer have the concaved buttons. I noted my PL2 which I now I bought last in 2004, has the small buttons and also use the same 8125 C&K... so note what you are after regarding the button, they both fit the same plunger:
small buttons for the Nimbs wooden cubes is C&K park 801802000 at 47 cents apiece (Accessory; Cap; P/B; Rnd; Blk; 8020; 8060; E010; E020; L; TP Series; 7.88mm Dia x 6.35mm H (This was what was used on my precipitation gauge circa serial number PC174) this is a smaller button then found on my wind monitor and barometer. I found that bigger recessed button also:
concaved larger button is C&K part # 752702000 which is Round, Concave Pushbutton Switch Cap Black Slip On its .25" tall and .375" wide and pushed on the .122 plunger. I believe these may have been used fIm ordering enough to make all my buttons match.
I did not take out a switch, but they are also C&K, if anyone ever needs replacement of those and obtains the replacement on those, they can post that below.
I am also purchasing a replacement battery case for the 4 C cells also available at allied as their stock # 70640173 for $1.99 each
Hope this is helpful.
73 de WX4GPS, Ron