Obsolete for 20 years, no longer available
SeaLand bought Mansfield in 1984...so any toilet that has Mansfield label is at least that old. SeaLand discontinued manual toilets almost immediately and discontinued all replacement parts for the 751...then discontinued 'em for the 752 a couple of years later. You're not likely to find any other pump assembly that'll fit your existing base...but even if you could, it would cost you as much as whole new toilet on sale. So the only question now is, which toilet. I think you'll find that most people here (me included) recommend the Raritan PH II (or PHC, which is the same pump on a compact base, if space is too tight for the PH II). It costs twice as much as the cheapest toilet...but is the only one that will last as least as long as your existing toilet has and will "swallow" flushes that choke most other toilets. Or...you have the best excuse you'll ever have to justify spending a bit more to upgrade to the "pushbutton convenience" of an electric macerating toilet...in which case, the Raritan SeaEra is by FAR the "best bang for the buck."