Hi Julia, I use a standard Draper gun which has served me well for fifty six odd years, there are several opinions on here and here is a grease gun link for you to muse over. At the end of the day it's a very basic tool as you will appreciate.
2009 4/4 Sport Henrietta 1999 Indigo Blue +8 2009 4/4 Sport Green prev 1993 Con Green +8 prev