> Interesting! Do you notice any problems on your Elnas' plastic gears?
What I usually do if I have not used one of the Elnas for a long time is to spray WD40 through the entire bobbin assembly to make sure its free, clean up any excess then oil all of the normal oiling points in the free arm. I use a mix of Singer sewing machine oil with an automotive teflon additive and it has worked really well, the machine smooths up and runs faster when it is fully oiled. I probably over service it but it only take about 5 minutes to take off the top and bottom plates and oil everything that moves so its no big deal and if I want to do a run of things I need it keeps the machine running at full speed with no other problems.
Most breakages come from things jamming AND trying to run the machine while it is jammed. Mine are a bit fussy about getting any threads caught in the bobbin casing and if it happens, immediately stop and untangle it. I have 2 as new Elnas with the cams and a couple of spares if I ever need parts but you try hard never to break anything on a machine that is near 50 years old.
Mine are the slightly earlier models called a SuperMatic, the SU is only very slightly different in the knobs and the internals are the same. I picked up the 2 very good ones from ladies in the country that has them from new and took great care of them.