Removing vBSEO - Reverting back to vBulletin URLs. Nginx 301-redirects.

[Fenriz]

Just uninstalled vBSEO from my vB 3.8.11 forum and got lots of 404 errors.
Please help with Nginx 301-redirects from vbseo-urls to vbulletin original urls.
I've read a thread https://www.unix.com/showthread.php?t=238951, with rewrite-examples but they are for Apache config file and I can't apply these changes to Nginx config file.

The main vbseo-rewrite rules (for Forums and Threads) were:
Forum:
f[forum_id]
Forum page:
f[forum_id]-[forum_page]/
Thread:
f[forum_id]/t[thread_id].html
Thread page:
f[forum_id]/t[thread_id]-[thread_page].html

I've tried to adopt some recommended rewrites (below) from one website, but it's not working for me:
location / {
rewrite f([\d]+)/ /forumdisplay.php?f=$1 break;
}

Following [myforum].com/f172/ I'm getting the page php-source downloading instead of the 301-redirect.

Please help me with the correct nginx 301-rewrites of the Forums and Threads pages.