In plain English
FAR 52.208-5, Condition of Leased Vehicles, is a contract clause prescribed at FAR 8.110, most recently dated Apr 1984. The complete official text is reproduced below, verbatim, from GSA's published FAR source files.
Its text contains no sentence requiring insertion into subcontracts; see the flowdown section below for what that does and does not mean.
Does it flow down to subcontracts?
No flowdown mandate found in the clause text
We scanned the full clause text and found no sentence directing the contractor to insert this clause into subcontracts. That is a statement about the text, not legal advice: a prime contractor may still flow terms down contractually, an agency supplement (DFARS, VAAR, …) may add requirements, and clauses listed below (if any) may order this clause into subcontracts from the outside.
Where it's prescribed
As prescribed in 8.1104(b), insert the following clause in solicitations and contracts for leasing motor vehicles, unless the motor vehicles are leased in foreign countries:
Prescribing reference: FAR 8.110.
The official text, verbatim
As prescribed in 8.1104(b), insert the following clause in solicitations and contracts for leasing motor vehicles, unless the motor vehicles are leased in foreign countries:
Condition of Leased Vehicles (Apr 1984)
Each vehicle furnished under this contract shall be of good quality and in safe operating condition, and shall comply with the Federal Motor Vehicle Safety Standards (49 CFR571) and State safety regulations applicable to the vehicle. The Government shall accept or reject the vehicles promptly after receipt. If the Contracting Officer determines that any vehicle furnished is not in compliance with this contract, the Contracting Officer shall promptly inform the Contractor in writing. If the Contractor fails to replace the vehicle or correct the defects as required by the Contracting Officer, the Government may-
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(a) By contract or otherwise, correct the defect or arrange for the lease of a similar vehicle and shall charge or set off against the Contractor any excess costs occasioned thereby; or
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(b) Terminate the contract under the Default clause of this contract.
(End of clause)