Some ather products could be use on RTJ flanges with good results and avoiding cracks and over stress within flanges:
http://www.garlock.eu.com/pdfs/Kataloge_GB/Gasketing_GB/OMICRON_GB_JAN-2000.PDF
http://www.pikotek.com/
You use packing graphite based "www.garlock.co.uk" if you don't have contact with oxygen(corrosion of graphite)
In some case you can use metallic seal. It depends on how the stem move