Repairing 12oz lamps can be difficult because the formula used in these lamps is one of the earliest formulas produced by Lava Lite and is likely to contain polychlorinated biphenyls (PCBs) which makes it unsafe to handle, but it comes with its own set of quirks that are not well understood due to the rarity of the formula and the inability to obtain the ingredients.
The surfactants used in this formula also seems to separate from solution and cloud the master fluid. Filtering the master fluid with ceramic filters damages the formula and will cause the wax to stick to the globe and cause master fluid bubbles in the wax. It may be possible to filter the master fluid and add a small amount of sodium lauryl sulfate to the master fluid before running the lamp. This is a solution that has only been proven to work 1 time though so beware before trying this option.
The master fluid inside has a density very close to water which means that these can only be topped off with distilled water and not with master fluid from another modern lava lamp.
Cleaning and Refilling With Original Formula
The best way to empty these globes is by draining the liquid into another container. Preferably a glass jar. Place the globe back on a base and melt the wax and then pour that into another jar or into a large hydroponic syringe if you have one. The syringes are preferable for a number of reasons. If using a jar or another container it is difficult to remove 100% of the wax from the jar. The older formula has a tendency to stick to glass if it is not coated in surfactant, but it also easily clouds if agitated in master fluid. The syringe allows the wax to be injected while cool which solves for all of the above issues. When done successfully it will look like a brain floating in the globe.
Cleaning the globe is difficult without bottle cleaning brushes. Due to the narrow opening not a lot of brushes will fit. Additionally the glass often has spots that require scrubbing to really fix. You can identify these spots using water. It will bead up on these spots instead of flow off of it when you turn the globe with water inside it.
The best way I have found is to use a combination of bottle brushes and paper towels with some water and degreaser such as Simple Green. Soak the paper towel in water, roll it up, and insert it into the globe. Pour some degreaser in the lamp and then insert the bottle brush and use it to move around the paper towels to get all spots that have water beading. Once water is no longer beading it will indicate the globe is ready to be refilled.
Refilling With Modern Formula
It is possible to refill these globes with formula from a Mathmos Neo globe. Fortunately this allows for the globe to be ran with a 15 watt bulb like they originally did and they will not overheat. Unfortunately the flow is not as lively as the original PCB based formula, but it is still far better than no lamp at all. Using the hydroponic syringe method is also recommended when using Mathmos Neo formula because Mathmos formula also has issues with wax sticking to the glass.
The Lava Library 