The jack socket on my 48k+ had a fault where you needed to hold the plug at a specific angle or it wouldn't make contact. You had to do that and remain motionless for the entire loading cycle. Something like 40% of the tapes I bought never actually loaded, and I was never sure if it was because I wasn't holding it right, or they were faulty out of the box.

And no, I never had the confidence at the time to take the lid off and see if I could fix it. It was just too precious to take the risk.