Plumber cam over today. Have a over 20 year old Delta-mix, I believe the Modal # is M 3494. The plumber had a really hard time getting the cartridge out. Had to use WD-40. Now he says it is too old to find a replacement cartridge and I should instead get a whole new faucet which he says will take 3 hours to install.Do you think this is valid? Do you have an opinion?

I believe two thing on this issue. He is taking you for a little ride and you need to check that model number a little better. I find no trace of that number and they do continue to make cartrdiges for even older models.

I have the 'same' and I used the spring/washer kit to fix a drippy faucet. It's delta KRP4993.

That said, this sucker is old, and it's not a terrible idea to have it changed-out.

Dcrandall, I see you are new to the site, did you notice this question was 4 years old?