The cylinder-heads on the machine this component suits have a lot more functions to carry out due to desmodromic (positive closing of the valves by mechanical processes rather than just valve springs) valve actuation, and every component involved needs careful inspection during refurbishment.
The valves, valve guides, collets and stem seals would normally be renewed in unison. Where a worn or damaged part is renewed try and renew, where possible, any interfacing components to help avoid premature wear or damage to those new components.
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