The most common and difficult to removed is grease/oil contamination,so I presume this is one of the reason why you asked for cleaning solvent without CTC.In our fleet, we're using LECTRA CLEAN (20 L/can) for cleaning motors which are heavily contaminated by over greasing of open type ball bearings. However..take note that one of the component of this compound is isoprophyl alcohol, where during evaporation it leaves condensation which we know is bad. As corrective measure,immediately after cleaning using this solvent, we usually introduce external heating overnight to ensure that the windings are dry then megger test and spray a light coat of insulating varnish (optional) before assembly.