There are alternatives, Aldo. You could turn up an adaptor that goes from an old low pressure grease gun or an oil gun to the thread on the gear case. Don't use a high pressure grease gun, you are likely to blow out some seals.
Here's is one of many available YouTube videos [which I should of included in my McCulloch M T1255 CLS Line Trimmer post] regarding Quick Feeding :"Tap'N Go" Brush Cutter Heads For Almost Any Make Of Model of Line Trimmer, on the market today.