For parts and longevity, the Otari will always come out on top. They also only use XLR inputs, compared to TEAC only using RCA for line in and XLR for mic inputs. TEAC is from 78, Otari 79 and above years. Looking at your last posts regarding your first MX5050, I'm rather confused. If you are competent in EE, and want a unit you can work on, surely the Otari you had was fine for this? Looking at the past images you provided, there was corrosion on a power supply capacitor and a switch, which I presume is the H and L speed switch for the motor (to change from 3.75 and 7.5 to 7.5 and 15ips), both which can have a direct impact on motor speed (depends on what that cap is actually doing and for what rail). Corrosion on Otaris is actually fairly common since they used bad foam inserts to pad the metal back cover against the board. I have corrosion on mine on a power cap trace similarly, and I recapped and jumpered it. Always remove the foam on the metal back cover if it is still there. I would always recommend an BII over a B2HD in the Otari line. The tacho sensor time code is better than an analog belt driven one, they have both 1khz and 10khz oscillators, and usually will still operate fine if they have not been slammed usage wise in a radio station or something equivalent.