I used to run coal and gas fired locos in the garden, and what eventually put me off was what I thought I wanted... Real coal...real oil.... real ash in the smoke box and ash pan! Give me the pretend stuff any time!!
However, because my locos carried out a lot of propelling stock through tight radius curves and point work I did, at one stage, grease the buffers with Molykote 1102 grease (used in the gas industry for greasing gas taps) but got fed up with getting it on my fingers and transferring to everything else in striking distance! It did look very realistic though.