Oil seal: get to know all the details about this timing chain kit component
Head Gasket and Valve Cover Gasket: Ensuring Engine Integrity
Most conventional oil seals are designed only to withstand very low-pressure applications (about 8 psi or less). If additional internal pressure is present or anticipated, pressure relief is necessary.

Oil Seal Manufacturing: Processes and Considerations
Spring The spring supplements the tightening force (i.e., the lip radial load) to ensure enhanced sealing performance and tight contact between the shaft and the sealing edge.The spring also prevents the deterioration of main lip sealing performance caused by high heat or other such factors.
Meanwhile, rubber-cased oil seals are used under conditions where a metal-cased seal can fail (for example, because of thermal expansion). Unlike the metal-cased type, these seals do not rust. Moreover, they can seal a lightly damaged housing better than metal-covered seals since, in high temperatures, rubber can provide a more stable sealability.