...I am in a similar boat. I did a clean reinstall of Windows Vista Business SP2 from a USB drive and installed the manual updates outlined in your post.
I was able to update automatically except it would not install KB4014984 which is April, 2017 Security and Quality Rollup for .NET Framework 2.0, 3.0, 4.5.2, 4.6 on Windows Vista SP2 and Server 2008 SP2 (KB4014984) . The error is:
0x800B0109. I looked it up and it says:
A certificate chain processed, but terminated in a root certificate which is not trusted by the trust provider...
Hi mikey8811:
My Vista SP2 laptop is at a remote location so I don't have access to it while I'm working from home (I'm posting from my Win 10 machine for now) but a
Speccy Free snapshot of my Vista SP2 machine I posted online on 12-Jul-2019 athttp://speccy.piriform.com/results/z2qoNAESuxQeYKCK2QGx3or shows that my KB4014984 for the .NET Framework installed successfully in April 2017. Re-boot and run a manual Windows Update a few times, and if the installation continues to fail with error 0x800B0109 after a few cycles of re-booting and manual Windows Updates
then let me know what error or warning you see when you download the standalone .msu installerfrom the Microsoft Update Catalog at http://www.catalog.update.microsoft.com/Search.aspx?q=KB4014984 Vista to your desktop (be sure you download the appropriate 32-bit or 64-bit installer for your OS) and then right-click and choose "Run as Administrator".
If the standalone .msu installer still doesn't work when you "Run as Administrator" then go to Control Panel | Programs | Programs and Features | View Installed Updates and search for the full KB number in the search box (e.g., "KB4014984"
and not a partial string like "4014984" - see a sample screenshot below) just to confirm this .NET Framework update is not already installed. I'm guessing that the manual reset of your Windows Update components you performed wiped your Windows Update history
at Windows Update | View Update History when the C:\Windows\SoftwareDistribution folders were re-built, and I don't think searching for a phrase like "Framework" at Control Panel | Programs | Programs and Features | View Installed Updates will find anything
[.NET Framework updates are generally listed there by KB number and a generic descriptor like "Update for Microsoft Windows (KBxxxxxxx)"] so it's much harder now to determine the KB number of the last .NET Framework that was successfully installed on your
computer.

The good news is that most Vista-compatible applications that actually require the .NET Framework don't need anything higher than .NET Framework v2 (built in to Vista) or v3.5 and should prompt you if a newer .NET Framework version like v4.5.2 is required
(see the old Lifehacker article What Is the .NET Framework, and Why Do I Need It?). That means that not having KB4014984
installed might not really be a serious issue for your in practical terms, especially if the software you run on your Vista machine doesn't even require a .NET Framework. I'll have to do more research, but the Package Details <here>
for KB4014984 in the Microsoft Update Catalog show that KB4014984 has been supersceded (replaced) by the Sept 2017 update KB4041086 for Windows Server 2008 SP2 (see image below). My Speccy profile shows this newer KB4041086 was never delivered
to my own Vista SP2 machine in Sept 2017 via Windows Update, but Windows Vista and Windows Server 2008 SP2 share very similar code (both are based on Windows
build 6.0.600x) and many Windows Server 2008 SP2 updates released after April 2017 can be manually installed on Vista SP2 machines. This is just speculation on my part for now, but you might be seeing this error 0x800B0109 if Windows Update
is confused about the correct supersedence chain of .NET Framework updates for Vista SP2 vs Windows Server 2008 SP2.
32-bit Vista Home Premium SP2 * Firefox ESR v52.9.0 * Norton Security v22.15.2.22 * Speccy Free Portable v1.32.740
HP Pavilion dv6835ca, Intel Core2Duo T5550 @ 1.83 GHz, 3 GB RAM, NVIDIA GeForce 8400M GS