Abstract <p>The service life of the shaft–seal joint in agricultural machinery affects the overall operating life of the assembly. An analysis of factors influencing the durability of the shaft–seal joint revealed the need to investigate the quality of forming the initial interference-fit range in the joint and its compliance with the dimensional interchangeability parameters specified in the design documentation at the assembly design stage. The study aimed to evaluate the probabilistic characteristics of dimensional dispersion for the inner diameter of the seal and the outer diameter of the gearbox flange of the YaMZ-239 transmission. The study examined 100 flanges and 100 seals of type 1.2–100 × 125–12. Measurements of shaft-end diameters were made using an SRP 100-0.001 lever caliper. A DIP-6 instrument with an NIIK-890 system determined the inner diameter of the seals. An assessment of the dispersion parameters of the surface dimensions of the YaMZ-239 gearbox output shaft for the 100<i>h</i>10 seal seat showed that shaft manufacturing achieved process accuracy higher than required, with satisfactory process centering and exhibited a shift toward correctable defects. An investigation of the inner diameter of the seals showed good accuracy of the diameter-forming process, satisfactory process centering, and a slight shift toward non-correctable defects; however, no actual defects occurred. The analysis of interference dispersion showed that the probable percentage of defective joints, as a durability characteristic, equaled 0.01%. The results demonstrate that the manufacturing accuracy of the parts forming the flange–seal joint meets the specified requirements. Therefore, engineers should attribute emerging problems with lubricant leakage from seals to the wear-resistance parameters of these parts and to an analysis of wear in the influencing dimensions that form the dimensional chain, where misalignment deviation and shaft radial runout relative to the seal diameter act as the initial closing links.</p>