any Ebay/Amazon on EXACTLY replacement for black plastic sheild fastners?

This is the kit I use. OEM quality. Not a cheap Chinese knock-off.

120pc TOYOTA LEXUS specific plastic push rivet-panel retainer kit DORMAN“Needa” | eBay

 

See Figure 51-02, Suspension Crossmember & Under Cover, click View More Images, and then select the second image, to see the ten clips (90467-07220) and four bolts (90119-06A13, now 90119-A0451) that secure the No. 1 Engine Under Cover.

Note that the 90467-07220 clips aren’t among those in the kit @Georgina Rudkus kindly linked above.

 

Toyota has several variations of these clips over the years. As long as they are either 7mm or 9mm, they will fit. Toyota uses 7 and 9mm as a standatd.

 

A while back I picked up a nice kit for removing push rivets and all manner of auto trim and other components. A very worthwhile investment (even includes an assortment of rivets) for $27:

 

I have not bought one for PP, but for our Honda and Nissan, the Rexka brand fasteners found on Amazon have worked very well. Honda OEM fasteners are exorbitantly expensive and I never bought the OEM parts as a replacement. I find removing those fasteners intact is often difficult, and I usually, break them as I try to remove them. Now I consider those fasteners to be non-reusable and replace them with new ones every time. For oil change which is done every 6 months or so on our other two cars, even cheaper non-OEM clips hold for that duration no problem as long as the size matches.

I believe 90467-07220 clips @Elektroingenieur mentioned is this.
Rexka 20 pcs Splash Shield Front Shield Under Cover Clip Compatible with 90467-07220 Toyota Lexus

 

If you’re referring to the gaskets for the transaxle filler and drain plugs, the Repair Manual (more info) says to use new ones, except when doing the specific steps in which one plug or the other is temporarily reinstalled.

 

You'd be just fin reusing the aluminum gasket washers. They will conform without problem.

 

It helps if you’re the only person dealing with them, and you wash them in hot/soapy water every time you have them out. I find a paint can lid pry tool works well, for prying up centre caps on the fasteners.

 

I think I read your suggestion on another thread and tried using the paint can lid opener, but I still ended up breaking most of the top round center cap. Using other tools was equally ineffective. For my son's Honda, if I am using an OEM clip @$4.72/pc, I would try to save them to re-use, but compatible aftermarket clips are cheap, like $9.99 for 100 pcs bulk bag. That's @$0.10/pc. Those aftermarket clips may not be as good as OEM, but for just holding light plastic underbody splash guards for ~6 months, they work fine. I have not yet to find a single missing clip ~6month to 1year after installation. It is that it tends to break even more easily than the OEM fasteners when trying to remove. For ~$1 per oil change job when the underbody cover has to be taken down, I just change all 10 clips with new ones. Without not caring to preserve the old clips, the removal process works much faster.

 

A lot of factors at play. For starters, I think your weather is a lot harsher, you have lots more road salt and sand, compared to here. I've also had the ours garage stored since new, and done all the oil changes: nobody else has monkee'd with the underpanel.

I take the underpanel off completely, with each (6 monthly) oil change, and with several additional removals, would guestimate it's been off around 25 times now. Unless I just had it off, I make a point of going in, washing the fasteners in the laundry sink, work the mechanism.

Sticking with that regimen, it took till 2019 (purchased in fall 2010) before I started seeing a broken tooth or two on the fasteners. Never had a broken cap, say due to mechanism jamming when you try to pry it up. I purchased a complete replacement set at that point, and have replaced a few (mark the caps with a silver X to differentiate), and so far I've used about 4~5.

Amayama order: