A little late to the party but I'll post anyway. I've had a Tandberg 10X from new and it needs a bit of work, recap I would suspect would bring it back to right. When I got it the tech at the shop set it up for Maxell UD35-180B the backcoated tape and I used that since I bought a box from Maxell. I also used some of the non-backcoated UD35-180. Tried a couple TDK Audua both backcoated and not and it was fine. Since I was working at a store that sold Maxell, it is most of my collection. A few years ago I bought a pile of reels from a company going out of business, Quantegy 406/456 tapes, including a box of pancakes. Sold most of it but kept the pancakes and a couple of the 456s. These are what I'm recording on now since I found a reasonably priced Crown SX-724 that needed a full nicotine cleaning bath, recap, maintenance and set up for the tapes I was using. I did the mechanical/recap and sent the electronics to Chuck Ziska with the headblock and he retouched the heads, mild relap, and set them up on his machine and dialed in the electronics to the tapes I would be using. That machine sounds just DAMN EXCELLENT, even playing the tapes I recorded in the late 70s/early 80s when I was more active using my Tandberg.
Get a machine that is in good shape, refurb it to like new and set it up to the tape you will be using and you will have something.
Pontificating Bob is totally correct on the purchase of used tapes, in general. The ones I bought were from a production house and if they had been recorded 8 times they were replaced. If they were more than 5 years old they were replaced hecne the reason they had a box of pancakes in the sell off. So I got some lightly used fairly recent tapes, not tapes used in a dirty environment with dirt and other detritus caked into the magnetic medium. So I quoted his third comment below.
The first comment is also very true. If you are going to use a specific tape have the machine dialed in for that tape. Back in the day this was done for batch lots of tape since the tapes were ordered by the multiple boxes. Not so much the home audio crowd which had machines that were rarely their best because they were never moved from factory settings by the happy and clueless owners.
Finally, Bob talks about the price of an NOS box of tape. Why on earth pay more for an NOS Maxell UD35-180B when you can buy new and better tape for less. Keep an eye on what tapes sell for and you will see the use of new tape is the way to go. Is it expensive,? NO, it is selling for exactly what tape sold for back in the day adjusted for inflation. Now if you are making the same today as in the 80s I understand your concern but tape isn't really expensive today.
Follow Bob's advice.
I'm not a fan of the NOS tapes but that's primarily because the prices for the good ones are now equal to or more than the new stuff. I prefer buying new and supporting the existing manufacturers these days.
...extracting the most out of a reel to reel (or a cassette) deck really means you need to spend the time (or in my case, the money) to properly calibrate the deck to a specific tape. Even if you have Bias and EQ switches on your deck(s), I still recommend setting the deck up for one specific tape you'll use most of the time.
Third: in a lot of cases, old acetate and early mylar tapes bought on the cheap are false economy.
Happy taping, folks.