I wanted to share a success story for anyone here who might need this information. I have a 217.585930 Gamefisher, 7.5hp, and it had a blown lower crankshaft seal. The pics show the condition of the destroyed seal. Sears, Brix, and CPC all list this lower seal (p/n 510318) as being no longer available. After some extensive research with a local part supplier in my area, Applied Industrial Products, I found that SKF seal #6608 is the exact size (17mm X 27mm X 7mm) as the original 510318 seal. Also, my crankshaft was badly scored and pitted, so before installing the new lower crankshaft seal, I installed a SKF 99068 Speedi-Sleeve over the worn crank, using a thin coating of Loctite marine epoxy under the Speedi-Sleeve. Problem solved. The pics show the fix.
On these forums, there have been some who question the integrity of these older Sears/Eska engines. After completely disassembling mine, I will say that the Tecumseh powerhead is every bit as robust inside as an equivalently sized OMC engine. These Sears/Eska engines are well made, and with a little ingenuity from outside part sources, it's possible to keep them running a long time.