I do not have mechanical expertise in the rebuild of exchangers and cannot provide you with any good “tricks”, however SGL Carbon Group manufactures this style of exchanger and you may be able to contact someone there to gather assistance. Try http://www.sglcarbon.com/gs/prodser/process/blockheat.html for more information and contacts. There may also be other manufacturers which you may be able to find on the Thomas Register web site at www.thomasnet.com.