Having never used PLA before, I immediately noticed upon first handling that it seems rougher and drier, than ABS.

However, as all good engineers, I ignored this fact and stormed on, on the basis that if it works for everyone else, then its bound to work for me.

The first few test prints I did went well and so I tried printing my early case design prototypes (just coarse approximations of shape and size at this stage).

After a couple of hours, the printer nozzle clogged and ruined the print. So I cleaned it out, following guides I found online and various YouTube videos. Then started printing again. Then it clogged and I got cleaning and then started printing again. Read this paragraph over and over whilst burning some money, several times.

Anyway, to cut a long project log entry short, 3 weeks went past with me disassembling, re-assembling, poking, cleaning, retracting, extruding, bed-heating, extruder cooling, tweaking settings, etc, etc.

No joy!

So, I sat back and thought back a few weeks. It was working and now it isn't. I changed nothing but the filament material. Hmmmm. The ABS was smooth and oily, the PLA is rough and dry. Hmmmmm. What if I oil the nozzle? Will it catch fire? Will it kill me? will it dissolve the filament or the print bed? What if it just works?!?!

The last one had me hooked. I removed the (cooled down) printer head assembly and put a drop of machine oil in the feed tube inside the head, re-assembled it and then extruded the PLA through it.

Yes, there was some visible smoke, but the extractor dealt with that. It cleared up within a minute or so. I extruded about 2 feet out of the nozzle for no reason at all.

Next, I tried printing my 3D models... they printed out perfect, no clogging, no residue, no staining. Perfect. 

Fantastic, I thought. But what about when the oil dries out? So, in order to maintain this level of reliability, I have made this checklist a habit when using PLA:

1. put a couple of drops of machine oil (mineral oil, bicycle oil, 3-in-1 oil, light oil) on a cloth or tissue
2. trim the PLA end and rub the oil onto the first inch-or-so of the filament. Let it "soak" a little.
3. Feed and extrude up to about a foot of filament.
4. Print stuff without fear of nozzle clogging.
5. withdraw the PLA when I have finished printing for the day