New TT or old

A record cleaning machine would make the most positive impact at this point.

Sell the B&O and scrape all the money together you can. Then buy a new (secondhand) recordplayer and cartridge, and spend some money, as Dean suggests, on a record cleaner.

In case you're not aware, the B&O cartridges are significantly better than the tables were and have garnered quite a following. They are only available now through an arrangement with Soundsmith, unless you luck into a NOS(new old stock) one. The sensible route would be to move to another table that affords more options but this adventure you've embarked on isn't necessarily about sense, although if you're not careful it can be about cents.

Another thought:

Turntable technology, at its best, has definitely evolved since the vintage of your gear. At the affordable end, though, you may still do better with an older design (at used prices). However, if you are willing and able to spend the money, you can do much better with new designs which are constantly raising the bar on both quality and price. Ditto re: cartridges. There are some very interesting evolutions available to us at this point on both fronts.

Although the best and most expensive tt's available today are superior to anything available 25 or more years ago, I would argue that at the low- and even the mid-price level you can get better quality reproduction for less money with a vintage turntable. Many of the modern "lower end" (if you think $2500 is low end) belt drives are nothing but me-too products. If you don't want to DIY, then buy a restored and upgraded product you can just plug in and use; you'll still pay less. Dual, Garrard, Lenco, Thorens, Technics, Kenwood, Sony, etc, direct drives and idler drives come to mind. Just my $.02.