I'm going to say roughly 15 years.... depending on the type of drive you've got. If you've done the gear drive upgrade on your NAK or if you have the "Cassette Deck model 1" that comes with gear drive, you're probably all right. Otherwise the drives do give out over time. Also I had a CR3a with a blown motor. My BX-300 failed and had to have the gear drive upgrade. I can tell you by perusing the ebay ads for naks that there are many CR-3a,CR-7a, others sold with some sort of drive problem.
How long do Cassette Decks last
Just a curious question. How long do you think a well cared for cassette deck will last. One of the better models from Nakamichi, Tanberg, Revox, Pioneer etc. Can anyone estimate the hours they have on their old pal? Thanks.