If you use a moderately viscous oil enough stays on the gears for most sessions. I don't know what oils Harrisons recommended, though it may be in the manual (mine is a photocopy bought from Tony Griffiths); but the saddle on an L5 / 5A is no different from most other lathes is being open underneath.

Some people use high-pressure bearing-grease on change-wheels, though not the saddle gearing. I just use oil, but I am not running either my L5 or Myford ML 7 so fast that they spin-dry the change- wheels.

I have found my L5's headstock is not especially oil-tight – but I think most emerges through the bearings. I keep a tray under the change-wheel guard to collect the oil that would otherwise end up on the floor.

Thinking about it, it is tempting to make a sloping "draining-board" to direct the oil dripping off the change-wheels into the chip-tray; but that would make the lathe much harder to clean and is probably not ideal if your lathe has a pumped coolant system.

To help keep the lathe itself clean, I cut some left-overs of ordinary plastic down-pipe lengthways to form gutters that are a gentle push-fit, held by their own elasticity, into the bed below the ways, under both headstock and tailstock. This is so swarf and oil-drips can be swept into the chip-tray instead of accumulating in the deep bed cavities.

As a by-product the gutter at the far tail end finds itself as a "hold-this-er" of small tools or work-pieces – as long as I remember they are there when pushing the tailstock back!

I don't know if the headstock on the 5A differs much from that on the 5, but on mine the only way to verify and replenish the oil level is to take off the cast aluminium cover, held on with two 1/4 inch BSF cap-screws.

Mine didn't have a cork gasket but a sheet of thick greaseproof paper I took to be original, though I can't be certain. The poor thing was practically dry though, when I investigated!

Some of the Harrison lathes had a combined filler/sight-glass, but not mine. I have acquired one but not yet determined the best place to fit it. It will need me to drill and tap an appropriate hole, but the difficulty is knowing how high above the headstock floor the red line needs to be.

What may be worth doing, given that these headstocks obviously need enough oil in them for the largest gear to dip into, is going a bit further than just drilling holes to drip oil through, by making and fitting a proper oil filler-plug with combined dipstick.

Provided the headstock is not leaking anywhere, it should not be necessary to drip oil into it regularly, but one leak path to be aware of is the threads of the screws that hold the unit to the bed. I had had to dismantle mine to move it, and I think I fitted fibre washers under the screw heads on re-assembly. Oil going down there disappears into the cavernous void below, and either oozes out into the chip-tray or seeps down the screws holding the machine to its cabinet, thence onto the floor.

If you give all the oil nipples on the saddle a shot of oil each time you use it, plenty of oil will work its way onto the gears.

Ditto the gearbox (mine also receives a certain amount of seepage from the headstock).