it's not wise to continue running a non detergent oil.
non detergent oils are for machines with no oil filter.
detergents suspend particles to be trapped into the oil filter.
low tech gas engine on small lawnmowers,a nd air compressor sumps with no filters get no detergents to keep the particles from being suspended, and rather to let them settle safely and not get into bearings.. etc.
I re-work PLENTY of antique tractors.
I don't care what was in it when i got it.. it gets 15w40 in it afterwards once I'm done, with some very, very limited exceptions.
depending on what the drainings look like, is how drastic a cleaning I do.
if it drains out like tar, then it gets a flush... 4 qts walmart 10w30 and a quart of f-atf fluid, plus a 2.99$ walmart filter... run till well warmed up, then drain.. after that, another new filter and real oil.
if you feel sludge at the bung drain.. i'd encourage you to drop the pan perhaps and clean it.. cost is time and a pan gasket.. also lets you look at the bottom of the engine...
I do similar with the tranny and hyds and rear end sumps.. except they get a flush of diesel and atf, and if they have water in them.. diesel + atf + 90% alcohol...
soundguy