Black Jack Asphalt and Tar remover is the product I've used to clean up any leftover residue of the 'cement' from the stainless tank trim. Just clean up the solvent with soapy water to remove the oily residue and then wipe the stainless trim with denatured alcohol and let dry before installing the new glass panes and silicone.
You will probably have to make some spacers to fill the gaps between the S\S frame and the glass to compensate for the removal of the old 'cement'.
Eheim Pimpette #270
Eheim Pro II 2028; Classics Series -2215, 2217, 2260, 2262; Pro 2229 Wet/Dry