How long does your RO membrane Last?

[this is me]

I have been running mine ever since I started the hobby. Almost 4 years ago. I probably make about 40gallon per month of RO/DI water. I've changed the Sediment, carbon, and the DI cartrige numerous times. But I never touched the RO membrane. It still producing 0 TDS water. Well, I went filter cartridges shopping today and I even got a second dual line TDS meter and probed it in the incoming line and the outgoing line of the RO membrane. The readings were 89 coming in and 0 coming out.
The rest of my RO/DI system TDS readings were,
79 coming from the faucet.
89 after the sediment and carbon block line. (is this possible? )
0 coming out of RO
0 coming out of DI

 

[Yaktop]

I guess it all depends how much comes out of your faucet. mine is well over a 100 and I make more water so measurably less. four years, a year at best for me. by the way its all respective, my system is 250 gallons so therefore more of everything.