it is understood,however,that if so instructed by the buyer,shipment under sub-clauses 1 and 2 above shall be made by air-freight and in the event that the seller dies nit take prompt action to fulfill its obligations hereunder, the buyer may ,without prejudice to any of its rights under the agreement,carry out the remedial work by itself and charge the seller for the costs of the work any parts supplied in replacement of the defective part of the goods or the goods repaired pursuant to the foregoing provisions shall be supplied and repaired on the same terms and conditions as provided herein for the supply of the goods and in particular a fresh warranty period shall apply