I'm going to replace the idler arm bushings tommorrow (the main pivot point for the steering linkage). When looking at this the other day, I noticed a plastic cap in an access hole that goes into the housing (attached to the frame) for the bushings and the main bolt. The access hole is about 1 inch in diameter, and the plastic cap is similar to the caps on jack holes. Does anyone know the purpose of this access hole??

Thanks

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)