Hi , 90k isn't really a lot for a vr engine providing that it has had quite regular servicing and a new timing chain and tensioner(mine went at 93k ,ouch!!!),if this hasn't been changed that should give you a bit of room for negotiation cos it will cost a bit of money to replace the tensioner because of the amount of time it takes ie high labour costs, the gearbox has to be taken out to take replace the tensioner which is going to be approx 8 hours labour , obviously different garages have different hourly rates, rust shouldn't be a problem, check for the usual too ie make sure the oil is oil