Aliexpress
There’re some similar items on Aliexpress in my database. There may be some other items though.
| Image | Product (link) | Price | Coupons |
|---|---|---|---|
 |
Automotive Brake Fluid Testing Pen | 3.41 USD | – |
 |
HT662 Brake Fluid Tester | 5.15 USD | – |
 |
Auto Brake Fluid Tester | 27.26 USD | – |
 |
Brake Fluid Tester | 30.74 USD | – |
More on Aliexpress…Here are coupons that you can use.
Latest price update (UTC time):
Banggood
Banggood warehouse is located in China. I found coupon for you. Check this out.
Link: Banggood product page
Coupon (12.05 USD): BGRepair63
(CouponsFromChina.com tip: this code has to be applied in your cart after clicking “Proceed to checkout”. Click to copy code and open shop)
Exclusive Allowance Coupons: https://bit.ly/3xWgD9k
Old coupons (from the oldest to the newest): BgAuMotor, TTxBG10, AM15prime, AMPrime01, Automo, Automo1, BGCHRISTMAS, BGCARPA, BG20CAR, BGAutos, bGhOnEy10, BG2dfcd7, BGCARELEC, BG32673, 13f142, BGAFF10OFF, BGCuponation10, BGHONEY2110, BG10OFFAFF, BGwhielabel, BGHRepair2, BG10OFFAFF1
(probably won’t work, but you can try them out)
Price history and price alert
Price history (for all/most countries) for Brake Fluid Tester Pen is here.
Price records source(s): Gearbest, Banggood
Click on image to enlarge. 
You can set price alert (for Banggood).