Ferrari 488 GTE (42125) is my first Lego technic set and I’ve noticed that some pieces differ in the shade of the red/maybe even the type of plastic and also don’t match the diagrams and pictures from other folks’ assemblies posted on the Lego.com. Is this a counterfeit concern and, overall, does this happen a lot with Lego technic as it does seem to be damaging the look?
According to Bricklink, the 42125 should contain 4 pieces of Technic, Axle and Pin Connector Perpendicular Double Split, which looks like the one the instructions show:
However, it has a mold variant* called Technic, Axle and Pin Connector Perpendicular Double Split, Reinforced Sides, which looks like the one you have:
Based on this, I'd say your set is probably authentic, just got parts from a different manufacturing batch due to mold transition or surplus pieces.
The occasional color variance between pieces in the same official set that are supposed to be the same hue is known for a long time, that doesn't indicate a counterfeit item.
If you want to be sure, you can consider how you have acquired this particular set: on one end of the spectrum, buying directly from LEGO.com 100% nets you an authentic one. On the other end, buying for a tenth of the official price from a noname pop-up webshop will almost guaranteed to be a knockoff. Other retailers and private sales occupy some position between these two.
You can also look for LEGO markings, which should be present on most pieces. If your set was new and sealed in a box, and you've found LEGO marked pieces, you can rest assured it is an original one.
Or you can contact LEGO directly to ask if that mold variant has ever been put into an official set of this model.
*Edit: a mold variant is a piece that has largely the same functionality, maybe with minor changes in possibilities or strength. See this article for several examples.
