Agreed, use no buffer oil.
Rhod, you should update https://www.thevespiary.org/rhodium/Rhodium/chemistry/peracid.html (https://www.thevespiary.org/rhodium/Rhodium/chemistry/peracid.html)
to reflect that... where it says:
Dry organic phase over 50g of anhydrous MgSO4 (made by baking epsom salts at 300°C for a couple of hours, let cool, then grinding into a powder) making sure to filter off the MgSO4, and washing the filter cake with a small amount of DCM. The solvent is removed and kept for a later run, the resulting residue is combined with 100ml of vegetable cooking oil and distilled under vacuum to yield ketone (>200 grams) [That is a 56%+ yield].
It should read:
The DCM is quickly distilled off with no vacuum and kept for a later run, the resulting residue is then distilled under vacuum to yield ketone (>200 grams) [That is a 56%+ yield].
There's no reason to dry DCM before distilling (water is azeotropically removed), and there is no reason to add a buffer oil to ketone (if it's polymerizing, that's because your vacuum sucks).