Hi mate tbf the focus rs engine itself is pritty solid as standard and very good for moderate power upgrades beware of slipping clutches though as mines just gone and have had the shock of my life at the prices of them and my flywheel has gone so has cost me around around the 850 mark with fitting it myself how ever they are a great car to drive and I doubt very much you will be dissapointed mate I am not every time my rs comes on boost a smile comes to my face and I personallly haven't seen any rot on arches on the rs focus I have seen a few on the tail gate on a few which is fairly common on all focus' my 1 has so far been a pleasure to own and would advise any 1 who's got 1 to go for it. Also check for gear box whines although the gear box on these things are very tough 9 out of 10 of these cars have been put through their paces and these can be costly aswell but as sed very very good car mate