Recalls 1 and 3 describe the same underlying defect (oil filter boss failure), and Recalls 2 and 4 describe the same underlying defect (countershaft oil seal failure). So there are two distinct issues, filed across four campaigns.
The 1979 Honda CB750 has 4 recalls, all involving engine oil leaks that can reach the rear tire and cause a sudden loss of traction.
Both issues affect the CB750K. The oil filter mounting boss can crack under engine heat, pressure, or over-tightening, causing the filter to come loose and drop oil onto the road or rear tire. Separately, the countershaft oil seal can split when the engine is repeatedly revved hard right after a cold start, allowing oil to leak onto the rear tire. In either case, if the rider doesn't notice the leak, the tire can lose grip without warning.