Weloveourcar

Hi, I'm a newbie, I have a problem with my near side rear suspension on an RX300 2003 model. We took the car to Lexus and they diagnosed the nsr height control sensor needed replacing, as they could t get a part u til next Tuesday, and the fact that we are on holiday Monday, I asked what could we do to get the part, they told me that they sell the genuine part on eBay and with next day delivery it could be done before Monday. The part arrived and I took it in. The next day, all fixed and collected the car, 13 mile trip home all back to normal. Our next trip out it reverted back to the original state, rang Lexus today's and they are trying to say it's the part, logically, it's highly unlikely? A brand new genuine part? Surely it's something else happening, we have to take it back on Monday, putting our holiday back and buying another part is another £218.... Help please?