Old Blogger Blog Posts Line Spacing Issue

Try this custom css:

.entry-content div {margin:30px 0}

Have a look in your Theme Options for a facility to enter custom css, but if there isn’t one you can use a plugin like this one:
https://www.ads-software.com/plugins/simple-custom-css/

Thank you lorro. Off all the answers to this problem I have tried, that seems to do the trick! It does seem to affect my page alignment on other pages, so I’m not sure if there is a way to have it only affect blog posts. But I will keep working on that as I am rebuilding my site anyway.

To get a style to affect only certain pages, you’ll need to find a common class in the body tag. Maybe:

.single-post .entry-content div {margin:30px 0}

or, on a page by page basis:

.postid-3036 .entry-content div {margin:30px 0}