.htaccess, Wordpress & vanity URLs

[admin]

I've been pouring over every Stack Overflow topic I can find on htaccess & vanity urls within Wordpress, but I'm completely stuck as to why mine isn't working. I'm a complete noob with htaccess, so I'm sure that has a lot to do with it.

I am trying to format all urls pointing to /dealers/dealers-info/username to the same wordpress page (id 112 - aka 'dealers-info') with the username as a parameter.

The vanity url code added is right after #vanity urls

For example, passing: URL.com/dealers/dealers-info/watergallery where 'watergallery' is the username, displays a basic 404:

Not Found

The requested URL /dealers/dealers-info/watergallery was not found on this server.

Any insight is greatly appreciated - thanks in advance for your help!

[EDIT - removed leading / and moved the rule - now seeing a WP 404 page]

Options +FollowSymLinks
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]

# add a trailing slash to /wp-admin

RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteRule ^uvmax/blog/$ /blog [R=301,L]
RewriteRule ^dealer-finder/$ /dealers [R=301,L]
RewriteRule ^sterilight/blog/$ /blog [R=301,L]

# vanity urls
RewriteRule ^/dealers/dealers-info/(.*)$ index.php?p=112&username=$1 [L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d

RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*\.php)$ $2 [L]
RewriteRule . index.php [L]