Long Term Trimix Usage

Hi folks, it has been a while since I was here! Following detection, I had surgery in Dec 2014 and radiation follow up in 2016. The nerve-sparing surgery apparently didn't actually spare them.
I started using trimix in the latter half of 2015 and had reasonable success, although I have raised the strength a couple times. Now in 2023 I have found a new problem which my Dr can't solve. Due to the lack of "normal" blood flow post surgery, I was warned early on that the cavernosal tissue would suffer from the lack of blood supply, but that the Trimix injections could reduce the damage somewhat.
What I have not heard about and/or read anything on is possible scar tissue. The Trimix injections generally result is sufficient response for sex. However, now I have started having a needle-refusal issue. As some folks have mentioned, the needles are very thin (which is a good thing for this use) but now about 75% of the time the needle does not penetrate into the cavernosal tissue, either completely refusing or with a bent needle.
I have talked with my Dr but he has no explanation, although we both believe it may be a buildup of scar tissue, after +/- 1000 injections.

Has anyone else used Trimix for this duration? If so, have you had any similar issues, or found any solution/work-arounds?
Any info is appreciated!!

Peter, thanks for the response. We have had a cross between rejections and bent needles, even trying multiple locations. At first I thought it might be an issue with the syringe needles (and sort of still wonder). However, one of my primary concerns is having the needle break off during the injection (no desire to try and explain to ER Dr/nurse 😂). When I tried to put one of the bent needles back in its cover it jammed and snapped off at the base. I was just glad it didn't fail during the injection effort! I have occasionally had the issue with the plunger as well, requiring slight withdrawal before the plunger will depress.
I have considered the autoinjector but worry that if the needle bends while trying to insert by hand, the added power of the injector might exceed the strength of the needle, leading back to my prior worry!
Unfortunately, I think the boat left the dock a long time ago for an implant! Also, based on the original surgery, that procedure wouldn't be on my to do list!