https://www.amazon.com/gp/product/B008BYPRRI/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1
GS500s best friend. Perfectly safe for using with direct contact with engine oil, will stay soft and rubbery for its life. never hardens or swells. save yourself the trouble with black/red RTV from the big box stores. SOME of us know about this stuff but, most do not.
it isn't cheap. but a tube of the stuff should fully rebuild 10 GS engines. so if you've got other bikes you work on too, its well worth the cost.
just a PSA.