Colon after volume IF booktype and series following volume directly

Question

I am currently trying to figure out how to replace the dot by a colon after volume if * the bibliography entry is a book AND * the volume nr is directly followed by series So instead of

Bd. 10.

I'd like it to be

Bd. 10:

In case the entry holds no series, it should still show the dot instead of a colon (like it is currently).

In case of articles it should stay as it is (see Hijiya-Kirschnereit). MWE

\documentclass{scrreprt}
\usepackage[onehalfspacing]{setspace}
\usepackage[main=ngerman, english]{babel}
%----------------------------------------------------------------------------
%   BIB
%----------------------------------------------------------------------------
  \usepackage[
    backend=biber,
    style=authoryear,
    sorting=nyvt
  ]{biblatex}
\renewcommand{\mkbibnamefamily}[1]{\textsc{#1}}
\renewcommand{\labelnamepunct}{\addcolon\space}
\DeclareFieldFormat{postnote}{#1}
\DeclareFieldFormat{multipostnote}{#1}
\renewcommand\postnotedelim{\addcolon\addspace}
\DeclareFieldFormat
  [article,inbook,incollection,inproceedings,patent,thesis,unpublished]
  {title}{#1\isdot}
% sets Volume, Number, Id
\newcommand*{\volnumdelim}{\addcomma\space}
\renewbibmacro*{volume+number+eid}{%
  \printfield{volume}%
  \setunit*{\volnumdelim}%
  \printfield{number}%
  \setunit{\addcomma\space}%
  \printfield{eid}}
\renewcommand\postnotedelim{\addcolon\space}
\DeclareFieldFormat{postnote}{#1}
\DeclareFieldFormat{multipostnote}{#1}
\usepackage{url}
\urlstyle{same}

% italic series
\DeclareFieldFormat[book,inbook,incollection,collection]{series}{\mkbibemph{#1}}
\renewbibmacro*{series+number}{%
  \ifboolexpr{not test {\iffieldundef{series}} and not test {\iffieldundef{number}}}
    {\printtext[parens]{%
      \printtext{=\addspace}%
      \printfield{series}%
      \setunit*{\addcomma\space}%
      \printfield{number}%
      \printtext{\addperiod}}
      \nopunct}
    {\printfield{series}%
     \setunit*{\addcomma\space}%
     \printfield{number}
     \newunit}}

\begin{filecontents*}{\jobname.bib}

@book{Doi.1978,
    author = {Doi, Yutaka and Sano, Tetsuji and Tanaka, Itsuo},
    year = {1978},
    title = {Senkyo seido},
    titleaddon = {Das Wahlsystem},
    keywords = {Election law;Local elections},
    volume = {10},
    publisher = {Gy{\^o}sei},
    location = {T{\^o}ky{\^o}},
    series = {Gendai chih{\^o} jichi zensh{\^u}},
    abstract = {},
}

@article{HijiyaKirschnereit.2009,
 author = {Hijiya-Kirschnereit, Irmela},
 year = {2009},
 title = {Rezension: Reading Food in Modern Japanese Literature.},
 journaltitle= {Monumenta Nipponica},
 pages = {415--418},
 pagination = {page},
 volume = {64},
 subtitle = {By Tomoko Aoyama},
 number = {2},
 abstract = {},
}   

@book{Ito.1978,
    author = {Itō, Masami},
    year = {1978},
    title = {Broadcasting in Japan},
    keywords = {Broadcasting   Japan},
    volume = {7},
    publisher = {{Routledge and Kegan Paul [for] the International Institute of Communications}},
    location = {London},
    series = {Case studies on broadcasting systems},
    abstract = {}
}

\end{filecontents*}
\addbibresource{\jobname.bib}
%----------------------------------------------------------------------------
%   MAIN
%----------------------------------------------------------------------------
\begin{document}
\nocite{*}
\printbibliography[heading=bibintoc,title={Literaturverzeichnis}]

\end{document}

Hope someone might have an idea :) Best!