Back in 1972, my very first stereo system consisted of a Miracord 50HII, along with a Marantz 2015 and a pair of Acoustiflex 3 way bookshelf speakers. While the Marantz and Acoustiflex's are long gone (really miss my Marantz)the Miracord has never quit. I have 5 TTs in all. But, I've always kept the Miracord hooked into the system and she sounds as good today as she did 40 years ago.
I agree with the advice on checking the idler wheel. There are places that will resurface it for you if it is shot.
As far as cartridge and question regarding Shure M91-ED...My table originally came with a mid-grade Empire with eliptical stylus. It sounded OK. But, like so many who had the Miracords and Duals, back then, I tried out the M91-ED and have to say that (and I have tried quite a few)for some reason, that unit sings with that cartridge. Until recently, I had a heck of a time finding a decent replacement stylus (I even tried the Ed Saunders styli...way overpricced). Quality was poor, cantilevers too thick...sound was just not there..until I found a seller on ebay (name is Dualparts)who had beautiful stylus replacements for vintage Shure cartridges. The cantilever is just as delicate as the original and my old Shure sounds as musical as ever on that TT. Just make sure that you get the stylus made in Japan. It costs approx $22 with shipping. Same results with stylus replacement for M95ED (I paid $26).
Also saw a question regarding removal of platter. Instructions were correct...remove spindle, hold down center for counterforce, and pull that heavy platter straight up. I will add this, however. If you set speed selector to 33, it will come off easier because it retracts the idler wheel from the inside of the platter bit more. If you have fine speed adjustment; back off all the way in negative direction and you get even a bit more wiggle room.