how do i get the weird black gunk and sawdust out from inside the handle and vents, it's packed in there

Diagnosis

The "black gunk" accumulating inside the Makita XRJ05Z is a composite byproduct of fine particulate sawdust, airborne metallic shavings, and lubricant migration. Because the XRJ05Z utilizes a high-RPM motor and a reciprocating action that creates significant vibration, the internal cooling fan acts like a vacuum, pulling ambient dust into the housing. Over time, this dust mixes with the microscopic grease that leaks from the gear housing or the carbon dust generated by the internal switching components, creating a sticky, conductive paste. This buildup is particularly dangerous because it settles on the heat sinks and around the trigger assembly. When the vents are packed, the motor cannot dissipate heat, causing the internal thermal protection circuit to trip or, in worst-case scenarios, leading to premature failure of the MOSFETs in the brushless controller. You can confirm the severity by checking if the tool feels excessively hot to the touch after only 2-3 cuts in hardwood or if the motor sounds "strained" (a higher-pitched whine) due to the restricted airflow.

How to Fix It

To thoroughly purge the tool without causing internal damage, follow this sequence:

1. Remove the 18V LXT battery immediately to break the electrical circuit and prevent accidental trigger pulls.
2. Use a high-pressure compressed air canister or an air compressor set to approximately 30-50 PSI. Do not exceed 100 PSI, as you can accidentally push debris deeper into the sealed gear housing.
3. Insert the thin nozzle directly into the primary intake vents located on the rear of the motor housing. Blow in short, sharp bursts rather than one long stream to "shock" the gunk loose.
4. Angle the nozzle toward the trigger housing. The XRJ05Z has a gap between the handle grip and the main chassis where sawdust often packs into a solid block; blow air through this gap to clear the trigger spring and switch.
5. Rotate the tool 90 degrees and blow through the side vents, ensuring you are blowing *out* toward the exterior of the tool.
6. If the gunk is too sticky for air alone, use a soft-bristle nylon brush or a clean paintbrush to agitate the vents while simultaneously applying air.
7. Use a vacuum cleaner with a crevice tool held against the vents while blowing air from the opposite side to capture the debris rather than letting it fly into your face.

If That Didn't Work

• Chemical Solvent Cleaning: If the gunk has hardened into a resin, dampen a cotton swab with 90% Isopropyl Alcohol. Gently scrub the accessible areas of the vents. The alcohol breaks down the grease-based binder of the gunk without leaving a conductive residue. Avoid using WD-40 inside the motor housing as it attracts more dust.
• Partial Housing Disassembly: If the trigger feels "mushy," you will need to remove the exterior casing screws (typically T10 Torx). Carefully peel back the plastic clamshell to expose the trigger assembly. Use a vacuum and a dry microfiber cloth to wipe away the sludge from the switch housing before reassembling.
• Contact Cleaner Flush: Use a non-residue electronic contact cleaner spray. Spray it directly into the vent openings to liquefy the grime, then immediately blow it out with compressed air before the solvent evaporates.
• Professional Bearing Service: If you notice a grinding sound along with the gunk, the debris may have entered the motor bearings. This requires a full teardown and a bearing replacement, which is best handled by a certified Makita service center to maintain the tool's seal.

Heads Up

• Avoid Water: Never use water or "wet" cleaning methods inside the handle or motor vents; this will cause immediate corrosion of the brushless controller and void your warranty.
• Battery Port Caution: When blowing air into the battery terminals, ensure the air is dry. Moisture in compressed air lines can cause a short circuit when the battery is re-inserted.
• Preventative Maintenance: To stop this from recurring, spend 30 seconds after every heavy-duty job blowing out the vents with a handheld duster.
• Check the Blade Arbor: While cleaning the handle, check the blade chuck for sawdust buildup; a clogged chuck can cause the blade to vibrate more, which actually increases the amount of dust sucked into the motor.